Class 10 Physics - Sources Of Energy

What are the limitations in obtaining energy from wind?

Wind Energy output is not constant . It varies during different times of the day and is seasonal,and having following limitations.
- Cant be controlled
- Initial Capital Cost is very high
- Wind Energy farms can be put up only in areas with some minimum wind speed
- Large areas are required for wind farms.

State whether the given statement is True or False.

Biogas is produced by aerobic fermentation of animal slurry.

Microbial conversion of organic matter to methane called Biogas has become attractive as a method of waste treatment and resource recovery. This process is anaerobic and is carried out by action of various groups of anaerobic bacteria.
Three basic points about this process are that most of the important bacteria involved in biogas production process are anaerobes and slow growing, a greater degree of metabolic specialization is observed in these anaerobic microorganisms and that most of the free energy present in the substrate is found in the terminal product methane. Since less energy is available for the growth of organism, less microbial biomass is produced and, consequently, disposal of sludge after the digestion may not be a major problem.

So, the given statement is false.

State any two advantages of a box type solar cooker.

The solar cooker is a device that cooks food without using any conventional cooking fuel or energy like cow dung straw, wood, coal, gas kerosene, or electricity. It converts sunlight into heat energy and cooks food.
Advantages of a solar cooker :
As solar cooker does not consume any conventional fuel or electrical energy, it saves fossil fuels, wood, electricity, etc. which are otherwise required to cook the food. It does not emit any smoke or smell and hence does not pollute the environment. There is thus no chance of causing cancer and affecting eyesight or lungs. It does not require constant attention while cooking and hence saves time which can be utilized for some other productive work. As it is a slow cooking device, it preserves the nutritional value of the food. It can be used for cooking three to four items at a time. There is no possibility of causing accidents like catching fire, bursting of gas cylinders, electrical shocks, etc., and hence is safe to handle.

State some way of reducing air pollution in homes.

There are few ways to reduce air pollution at home:

1. Avoid smoking indoors (but quitting smoking is the best answer for overall health).

2. Use craft supplies in well-ventilated areas.

3. Make sure your gas stove is well-ventilated.

What is nuclear energy?

Nuclear energy is energy in the nucleus (core) of an atom. Atoms are tiny particles that make up every object in the universe. There is enormous energy in the bonds that hold atoms together. Nuclear energy can be used to make electricity.

What are the qualities of an ideal source of energy?

The qualities of an ideal source of energy are as follows:

1. Which librate large amount of energy per unit volume or mass.

2. Be easily accessible.

3. Be easy to store and transport, and

4. Perhaps most importantly, be economical.

What are fossils?

Fossils are remains, tracks, impressions, or traces of organisms that existed in the past. These remain embedded in volcanic ash, sedimentary rocks, peat, amber, etc., and get preserved and are an important tool for evolutionary studies.

Mention the names of any two types of fossil fuels.

Coal and petroleum are two types of fossil fuels, formed in the geological past from the remains of living organisms.

(a) Write names of any two conventional sources of energy.
(b) Write any two limitations in harnessing wind energy.

1. Oil, gas and coal are some conventional sources of energy.

2. Here are some limitations in harnessing the wind energy :
i. The speed of wind must be high (min. 15km/hr).
ii. Cost of setting up a wind farm is high.

iii. Availability of land as per the requirements i.e. large lands in hilly regions with high wind speed.

What are the characteristics of good sources of energy?

Characteristics of a good source of energy:
1) It should provide large amount of energy per unit mass (high calorific value)
2) It should be easily accessible
3) It should provide energy for maximum period of time and it should be renewable
4) It should be sustainable and safe (pollution free) for the environment.

Coal is the _______ source of energy.

Coal is the non-renewable source of energy.As it can not be renewed once exhausted.

Write any four benefits of using solar cooker.

Benefits of use of solar cooker:

(i) Fuel is saved as there is no requirement of any fossil fuel,

(ii) Does not cause any type of pollution,

(iii) No cost of maintenance which results in saving,

(iv) Food is formed which is tasty and nutritious,

(v) No possibility of burning of food

(vi) Four-five food products can be cooked at the same time.

Write four characteristics of the good source of energy.

Characteristic of good source of energy:
1)It should provide large amount of energy per unit mass .
2)It should be easily accessible .
3) It should provide energy for maximum period of time and it should be renewable.
4)It should be sustainable and safe for individuals.

Which type of energy sources are fossil fuels? Write down any two names of fossil fuels.

Fossil fuels are limited in nature and are non renewable sources of energy.
Coal and Petroleum are examples of fossil fuels.

Hydroelectric power plants are more ecofriendly than thermal power plants. Justify this statement.

Hydroelectric power plants generate little or no waste (hazardous) at all, emits no toxic gases when compared to thermal power plant causing lesser harm to environment.
However it is to be kept in our mind, that construction of dams often cause loss of biodiversity which needs to be taken account of and mitigated through environmental management.

What are the renewable and non-renewable sources of energy?

The sources which produce energy from natural resources, such as sunlight, wind, rain, tides and geothermal heat, which are renewable (naturally replenished) are called renewable sources of energy.

Eg.: Solar power, Tidal power, Hydroelectricity

Non-renewable sources of energy are the sources which produce energy from non-renewable resources that will run out or will not be replenished in our lifetimes, or even in many, many lifetimes. Most non-renewable energy sources are fossil fuels.

Eg.: coal, petroleum, and natural gas.

What is the main source of energy for earth?

Sun is the main source of energy on earth. It provides energy in form of heat and light

Name the agent which decomposes animal dung into biogas.

Anaerobic bacteria.

What are fossil fuels?

Fossil fuels are made from decomposing plants and animals under the earth millions of years ago. These fuels are found in the Earth's crust and contain carbon and hydrogen, which can be burned for energy. Coal, petroleum, and natural gas are examples of fossil fuels.

Name the two devices that work using heat energy of the sun.

The two devices that work on the energy of the sun are solar cookers and solar cells for electricity.

How does the excessive use of fuels in-fluence global warming? Explain.

Excessive of fuels produce greenhouse gases which increase the temperature of atmosphere and cause global warming.

Why is there a need for harnessing non-conventional sources of energy? How can energy be harnessed from the sea indifferent ways?

Conventional sources of energy are limited. They are rapidly being used up and will be exhausted soon. Therefore, there is a need for harnessing non-conventional sources of energy.
Energy from Oceans: It is a potential source of renewable energy. There are many forms of ocean energy.
(1) Ocean Thermal Energy (OTE): There is always a temperature difference between water at the surface and at a deeper level up to $$20^o C$$. By exploiting this temperature difference one can harness energy. This form of energy is called ocean thermal energy which can be converted into electricity.

(2) Sea-Waves Energy: Energy from oceans is also available in form of sea waves. Due to the blowing of wind on the surface of the ocean. It has lot of kinetic energy due to high speed. It can be used to produce electricity.

(3) Tidal Energy : The rise of ocean water due to attraction of moon is called 'high tides' whereas fall of ocean water is called 'low tides'. The tidal waves rise and fall twice a day. The enormous movement of water between 'high tides' and 'low tides' provides a very large source of energy in the coastal areas of the world.

(4) Energy from Salinity Gradient in Seas : The concentration of salts in water of different seas is different. The difference in concentration of salts in the water of two different seas is called 'salinity gradient'. The difference is concentration of salts where water from different seas meet can be used to obtain energy in usable form.

(5) Energy for Sea-Vegetation or Biomass : Sea-Vegetation or biomass is another indirect source of energy from the oceans. For example, the vast amount of sea-weeds present in oceans may provide an endless supply of methane as fuel in future.

What are the disadvantage of using fossil fuels ?

The disadvantage of using fossil fuels are:

i. Air pollution

ii. The oxides of carbon, nitrogen, and sulphur that are released on burning fossil fuels are acidic oxides. These lead to acid rain which affects our water and soil resources

iii. Global warming- the greenhouse effect of gases like carbon dioxide.

iv. The fossil fuels are non-renewable sources of energy

What are the environmental consequences of using fossil fuels?Suggest the steps to minimise the pollution caused by various sources of energy including non-conventional sources of energy.

Many of the environmental problems our country faces today result from our fossil fuel dependence. These impacts include global warming, air quality deterioration, oil spills, and acid rain.

Among the gases emitted when fossil fuels are burned, one of the most significant is carbon dioxide, a gas that traps heat in the earth's atmosphere. Fossil fuels are also implicated in increased levels of atmospheric methane and nitrous oxide, although they are not the major source of these gases.
Several important pollutants are produced by fossil fuel combustion: carbon monoxide, nitrogen oxides, sulfur oxides, and hydrocarbons. In addition, total suspended particulates contribute to air pollution, and nitrogen oxides and hydrocarbons can combine in the atmosphere to form tropospheric ozone, the major constituent of smog. Carbon monoxide is a gas formed as a by-product during the incomplete combustion of all fossil fuels.
Production, transportation, and use of oil can cause water pollution. Oil spills, for example, leave waterways and their surrounding shores uninhabitable for some time. Such spills often result in the loss of plant and animal life. Coal mining also contributes to water pollution. Coal contains pyrite, a sulfur compound; as water washes through mines, this compound forms a dilute acid, which is then washed into nearby rivers and streams.
During the electricity-generation process, burning fossil fuels produce heat energy, some of which is used to generate electricity. Because the process is inefficient, much of the heat is released to the atmosphere or to water that is used as a coolant. Heated water, once returned to rivers or lakes, can upset the aquatic ecosystem.

Following steps can be suggested to minimize the pollution caused by various sources of energy:

Avoid misuse of energy can reduce the energy consumption.
Alternative sources of energy like solar energy, wind energy, hydro energy and energy of sea should or non-renewable source of energy.
Use of smokeless appliances, Refined technology, Judicious use of energy etc.

What type of mirror is used in solar cookers and why?

Concave mirrors are used in solar cookers. The reasons are:

1. Concave mirrors absorb all the incident light and reflect it to a single focal point.

2. This reflected light is very powerful because it carries a lot of thermal energy.

Air gets polluted by the burning of large amounts of ............. in thermo-electric plants.

The combustion of coal contributes the most to acid rain and air pollution, and has been connected with global warming. Due to the chemical composition of coal there are difficulties in removing impurities from the solid fuel prior to its combustion. Modern day coal power plants pollute less than older designs due to new scrubber technologies that filter the exhaust air in smoke stacks; however emission levels of various pollutants are still on average several times greater than natural gas power plants. In these modern designs, pollution from coal-fired power plants comes from the emission of gases such as carbon dioxide, nitrogen oxides, and sulfur dioxide into the air.
Hence, Air gets polluted by the burning of large amounts of coal in thermo-electric plants.

What is biomass?

$$\textbf{Explanation:}$$

Biomass is renewable organic material also used as an organic fuel. It is used to create electricity or other forms of energy.

What is a wind mill ? Write any two uses of a wind mill.

A windmill is a structure used to harness the power of the wind for purposes like grinding grain, pumping water, and generating electricity. Wind causes the blades of a windmill to spin, these blades are connected to the shaft of a generator and the generator generates electricity.This electricity is used for pumping water or grinding grain.

What are the two disadvantages of fossil fuels?

The main disadvantages of fossil fuels

1) They do not last for a long time and can be extinct soon.

2)They release harmful gases which pollute the atmosphere mainly $$CO_2$$ gas

3) Oil spillage is another major problem as it hinders the life of many aquatic organisms.

What are the limitations of extracting energy from
(a) wind
(b) waves
(c) tides

(a) The wind:
1. Wind energy farms can be established only at those places where wind blows for the greater part of a year.
2. The wind speed should also be higher than 15 km/h to maintain the required speed of the turbine.
3. Establishment of wind energy farms require large are of land.
These are the limitations of extracting energy from the wind.
(b) Limitations of extracting waves energy: The waves are generated by strong winds blowing across the sea. Wave energy would be a viable proposition only where waves are very strong.
(c) Limitations of extracting tidal energy: The locations where such dams can be built are limited.

Compare and contrast bio-mass and hydro electricity as sources of energy.

$$ \textbf{Bio-mass}$$: Cow-dung, various plant materials, like the residue after harvesting the crops, vegetable waste and sewage are decomposed in the absence of oxygen to give biogas. Since the starting material is mainly cow-dung, it is popularly known as 'gober gas'. Bio gas is produced in bio-gas plant.
Bio gas is an excellent fuel as it contains up to 75% Methane. It burns without smoke, leaves no residue like ash in wood, charcoal and coal burning. The slurry left behind is removed periodically and used as excellent manure. This is one of the renewable source of energy.

$$ \textbf{Hydro Electricity}$$: In order to produce hydro electricity, high rise dams are constructed on the river to obstruct the flow of water and thereby collect water. The water level in the dam rises and in this process the kinetic energy of flowing water, gets transformed into potential energy. The water from the high level in the dam is carried through pipes to the turbine, at the bottom of the dam. Since the water in the reservoir would be refilled each time it rains. We would not have to worry about hydro electricity sources getting used up the way fossil fuels would get finished one day.

What are the environmental consequences of the increasing demand for energy? What steps would you suggest to reduce energy consumption?

Industrialization all over the world has increased energy demands significantly. Fossil fuels are used in large quantities to fulfill these energy demands. Large amount of carbon dioxide is released in the atmosphere by burning of these fossil fuels and this also causes global warming.

Therefore we should not waste energy and use these resources optimally. We should try to use alternate sources of energy wherever possible.

Fill in the blanks with suitable answer
Light energy can be converted into electricity by ____________

In a photocell when light strikes a semiconductor material , the semiconductor causes the electrons to flow which creates electricity. Solar power generating systems uses this concept of converting light energy into electrical energy. Thus a $$photocell \ converts \ light \ energy \ into \ electrical \ energy.$$

The basic source of wind energy is __________.

The source of wind energy is wind blow.

When the wind blows, it rotates the blades of a wind mill by converting the kinetic energy to the rotational energy of the blades. This rotational energy will then be used to generate electricity.

Correct the mistakes, if any, in the following statements:
(a) A good source of energy would be the one which does a small amount of work per unit volume of mass.
(b) Any source of energy we use to do work is consumed and can be used again.

Both statements are wrong.

(a) A good source of energy would be the one which would do a large amount of work per unit volume of mass.

A good source of energy is one that is:

1. easily available

2. easy to store and transport

3. will do a large amount of work per unit volume of mass

4. cheap and economic.

(b) Any source of energy we use to do work is consumed and cannot be used again.

Instead of using biomass directly as fuel, it is always advantageous to use biogas produced from biomass.
a) What do you mean by biomass?
b) What are the advantages of using biogas as fuel?

$$(a)$$ The dead parts of plants and trees as well as the waste materials of animals are called biomass. It is the organic matter which is used as a fuel to produce energy. Examples of biomass are cow dung cake, dry leaves, firewood, animal excreta, vegetable wastes and weeds. Biomass is a renewable source of energy because it can be produced again as it is obtained from plants or animals.
$$(b)$$ The advantages of using biogas as fuel are:

Household wastes and biowastes can be disposed off usefully and in a healthy manner.
Reduces the use of wood and in a way prevents deforestation.
The slurry from a biogas plant serves as manure.
Biogas burns without smoke and hence does not cause air pollution.
It produces a large amount of heat per unit mass.
It burns completely without leaving any residue. It is a clean fuel.
It is cheaper than most common fuels.
It is a good domestic fuel.

Write the energy conversion that takes place in a hydropower plant.

The potential energy of the of water in the reservoir gets converted into the kinetic energy of the flowing water. The flowing water rotates the turbine shaft connected to the generator which produces electricity. and Thus kinetic energy of water transforms into the mechanical energy of turbine which further gets converted into the electric energy.

Write about ocean thermal energy.

Ocean thermal energy conversion (OTEC) is a process or technology for producing energy by harnessing the temperature differences (thermal gradients) between ocean surface waters and deep ocean waters.
Energy from the sun heats the surface water of the ocean. In tropical regions, surface water can be much warmer than deep water. This temperature difference can be used to produce electricity and to desalinate ocean water. Ocean Thermal Energy Conversion (OTEC) systems use a temperature difference (of at least 77o Fahrenheit) to power a turbine to produce electricity. Warm surface water is pumped through an evaporator containing a working fluid. The vaporized fluid drives a turbine/generator. The vaporized fluid is turned back to a liquid in a condenser cooled with cold ocean water pumped from deeper in the ocean. OTEC systems using seawater as the working fluid can use the condensed water to produce desalinated water.

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What is geothermal energy?

Geothermal energy is heat energy generated and stored in the Earth.

Geothermal energy is generated at the geothermal power plants where the heat of earth is used to generate electricity.
Due to some geological changes, the molten rocks present in the core of the earth are pushed to the earth’s crust. Steam is generated when the underground water comes in contact with these points forming hot springs. This trapped steam is used to generate electricity in the geothermal power plants.

Why is tidal energy not likely to be a potential source of energy?

The tidal energy is not likely to be a potential source of energy because:

Only a few sites are available around the world which is suitable for building field barrages, and the rise and fall of seawater during high and low tides is not enough to generate electricity on a large scale.

State the principle of working of ocean thermal conversion plant. Explain how the plant works ? write one essential condition for it to operate properly.

Principle of working of OTEC: The water at the surface of the ocean is warmer than the water at deeper depths. This temperature difference can be used by Ocean Thermal Energy Conversion (OTEC) systems to generate electricity.
Working of OTEC:

In OTEC plant, the energy of warm surface water is used to convert low boiling point liquid ammonia into gaseous state.
The vapour of ammonia at high pressure is used to spin the turbines of generators converting the Ocean thermal energy to electricity.
The used vapour pass through the condenser where cold water, pumped from the deeper parts of ocean condenses ammonia vapour back into a liquid.
This process is repeated again and again to get continuous production of electricity. Essential condition for it to operate properly: The temperature difference between the warmer water at the surface and colder water at depths up to $$2 \ km$$ should be $$293 \ K$$ or more.

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What are the advantages of nuclear energy?

1. In a nuclear reactor designed for electric power generation, such nuclear fuel can be part of a self sustaining fission chain reaction that releases energy at a controlled rate.
2. By nuclear Energy large quantity of electricity can be generated.

Why many nuclear power plants could not be installed in our country. Give two reasons.

1. Our country still lacks the proper facilities that are required for the proper installation. Still being a developing country, one has to be sure of the proper facility availability to start this project.

2. The people of our country retaliate on its installation as they fear from the hazardous effect it would have as nuclear waste requires proper disposal. If not done so, the harmful gamma rays released have a cancerous effect and can cause mutations. Though this problem is in every country, but we lack facilities that are our biggest weakness.

"Burning of fossil resultant in global warming" Give reasons to justify this statement.

When fossil fuels are burned, they release large amounts of carbon dioxide, a greenhouse gas, into the air. Greenhouse gases trap heat in our atmosphere, causing global warming. Already the average global temperature has increased by $$1^{\circ}C$$.

Which process is responsible in hydrogen bomb?

The hydrogen bomb is based on a thermonuclear fusion reaction. A nuclear bomb based on the fission of uranium or plutonium is placed at the core of the hydrogen bomb. This nuclear bomb is embedded in a substance that contains deuterium and lithium. When the nuclear bomb (based on fission) is detonated, the temperature of this substance is raised to $$10^7\ K$$ in a few microseconds. The high temperature generates sufficient energy for the light nuclei to fuse and a devastating amount of energy is released.

What is the source of energy in the sun?

The source of energy of the sun or stars is the nuclear fusion of light nuclei such as hydrogen present in their inner part at a very high temperature and a high pressure. This results the formation of helium nucleus with a release of tremendous amount of energy.

What is a good source of energy?

A good source of energy would be one.
1. Which would do a large amount of work per unit volume or mass.
2. be easily accessible.
3. be easy to store and transport

4. perhaps most importantly, be economical.

What is wind mill? Write its advantages.

A windmill is a mill that converts the energy of wind into rotational energy by means of vanes called sails or blades.

Advantages of Wind Power:

It's a clean fuel source. Wind energy doesn't pollute the air like power plants that rely on combustion of fossil fuels, such as coal or natural gas.
Wind turbines don't produce atmospheric emissions that cause acid rain or greenhouse gasses.
It's sustainable. Wind is actually a form of solar energy. Winds are caused by the heating of the atmosphere by the sun, the rotation of the Earth, and the Earth's surface irregularities. For as long as the sun shines and the wind blows, the energy produced can be harnessed to send power across the grid.
Wind turbines can be built on existing farms or ranches. This greatly benefits the economy in rural areas, where most of the best wind sites are found. Farmers and ranchers can continue to work the land because the wind turbines use only a fraction of the land. Wind power plant owners make rent payments to the farmer or rancher for the use of the land, providing landowners with additional income.

Explain the principle of working of a thermal power plant. Draw a labelled diagram to illustrate your answer.

In a thermal power plant, heat produced by burning coal is used to boil water to form steam. The steam, at high temperature and pressure, rotates the turbine and its shaft, which drives the generator to produce electricity.
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What are the various fuels which are used to generate electricity in a thermal power plant.

Fossil fuels, LNG(liquid natural gas), coal or crude oil are the various fuels used to generate electricity in a thermal power plant.

What are the various steps which can be taken to control (or reduce) pollution caused by burning fossil fuels ?

Pollution caused by the burning of fossil fuels can be controlled by the increasing the efficiency of combustion process and by using various techniques to reduce the escape of harmful gases and ash into the surrounding air.

Write a short note on the pollution caused by burning fossil fuels.

Burning of fossil fuels leads to the production of many acidic gases like sulphur-dioxide and nitrogen dioxides. These gases causes acid rain which damages trees, plants and buildings, reduces fertility of soil, and poses danger to aquatic life. The burning of fossil fuels puts a poisonous gas carbon monoxide in air. It also produces large amount of $$CO_2$$ gas which damages the environment in the long run by increasing the greenhouse effect. Also, burning of fossil fuels produces smoke and a lot of ash.

State any four characteristics of a good source of energy.

A good source of energy is one:
(i) which would do a large amount of work per unit mass,
(ii) which is cheap and easily available,
(iii) which is easy to store and transport,
(iv) which is safe to handle and use.

Give one example of a good domestic fuel.

LPG.

What we the disadvantages of burning fossil fuels ?

Disadvantages of burning the fossil fuels are.
(i) The burning of fossil fuels produce acidic gases
(ii) The burning of fossil fuels produce large amount of $$CO_2$$ gas, which increases greenhouse effect
(iii) The burning of fossil fuels produce smoke and leaves behind a lot of ash.

Name the device which converts sunlight into electricity.

Solar cells convert solar energy into electricity. A typical cell develops a voltage of $$0.5–1\ V$$ and can produce about $$0.7\ W$$ of electricity when exposed to the Sun.

How has the traditional use of energy of flowing water been modified for our convenience?

Traditionally, the energy of flowing water has been used for rotating the water-wheels and for driving water-mills to grind wheat to make flour. The traditional use of energy of flowing water has been modified by improvements in technology and it is now used to generate electricity.
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How has the traditional use of wind energy been modified for our convenience?

Traditionally, wind energy was used through windmills to pump water from a well and to grind wheat into flour. But the traditional use has been modified and now it is used for the generation of electricity.

A hydro-power plant converts one form of energy into another. Name the two forms of energy.

A hydro power plant station converts the potential energy of water stored at large heights into electrical energy that can be use in homes and businesses .This stored water when falls on turbine rotates the blades of generator and generator generates electricity.

A hydro power plant converts one form of energy to another. the two forms are potential energy and electrical energy.

What is hydroelectricity ? Explain the basic principle of generation of hydroelectricity with the help of a labelled diagram.
(b) State two advantages of producing hydroelectricity.
(c) State two disadvantages of producing hydroelectricity.

(a) The electricity generated from hydro power plant is known as hydro electricity. Water is collected in a reservoir at a height, so the water has potential energy stored in it. When the water flows down through this large height, its potential energy gets converted into kinetic energy. The fast flowing water rotates the turbine which is connected to generator through its shaft. The generator produces electricity.

(b) Advantage of producing hydroelectricity

(i) It does not cause any environmental pollution.

(ii) It uses the energy of flowing water, which is a renewable source of energy

(i) Large areas of land are required.

(ii) Large eco-systems get destroyed.

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Name any three forms of energy which could be harnessed from the sea.

Three forms of energy that could be harnessed from the sea are:
(i) Tidal energy
(ii) Wave energy
(iii) Ocean thermal energy.

Flowing water can rotate a turbine. Which type of energy is used up by the turbine ?

Any object in motion has kinetic energy. So flowing water has kinetic energy and this flowing water when hits turbine blades , blades start to rotate and due to electromagnetic induction process Electricity is produced. So the energy used up by turbine is Kinetic Energy.

(a) What is the difference between a thermal power plant and a hydro power plant ?
(b) Which of the two causes serious air pollution and how ?

(a) Difference between thermal power plant and hydro power plant :
Thermal power plant uses non-renewable sources of energy Like coal, oil or gas. whereas hydro power plant uses renewable source of energy i.e. water.
Thermal power plant causes pollution due to the burning of fossil fuels, whereas hydro power plant is environment friendly.
(b) Thermal power plant causes serious air pollution because it emits harmful gases and fty-ash into the air.

What name is given to the heat energy obtained from hot rocks inside the earth ?

Geothermal energy.

What is wind ? What type of energy is possessed by wind ?
(b) Explain how, wind energy can be used to generate electricity. Illustrate your answer with the help of a labelled diagram.
(c) State two advantages of using wind energy for generating electricity.
(d) Mention two limitations of wind energy for generating electricity

(a) Moving air is known as wind. Wind possesses kinetic energy.
(b) The fast-moving wind strikes the wind turbine which starts rotating. The shaft of the wind turbine also rotates and drives the generator which produces electricity.
(c) Advantages of using wind energy for generating electricity:
(i) It does not cause any pollution.
(ii) It is available free of cost.
(d) Limitations of wind energy
(i) Wind energy farms cannot be established everywhere. They can be established only at those places where the wind blows for the most part of the year.
(ii) Wind energy farms require a large area of land for their establishment.
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Fill in the following blanks with suitable words :
(a) Biomass is another form in which ..... energy manifests itself.
(b) Tidal waves build up and recede .... a day.

Biomass is another form in which solar energy manifests itself as all the trees which provide biomass used sun's energy to grow.

Tidal waves build up and recede twice a day.

What is biomass? Give three examples of biomass.

(a) The dead parts of plants and trees, and the waste material of animals are called biomass It is the organic matter which is used as a fuel to produce energy. E.g., wood, agricultural wastes, and cow dung.

What is the function of anaerobic micro-organisms such as anaerobic bacteria in a biogas plant ?

Anaerobic bacteria help in the degradation of cow-dung in the presence of water but in the absence of oxygen.

(a) Explain how tidal energy can be used to generate electricity.
(b) Why is tidal energy riot likely to be a potential source of energy ?

During high tide, when the level of water in the sea is high, sea-water flows into the reservoir of the barrage and turns the turbines. The turbines then turn the generator to produce the electricity. And during the low tide, when the level of sea-water is low, the sea-water stored in the barrage reservoir is allowed to flow out into the sea. This flowing water also turns the turbines and generates electricity.
(b) Tidal energy is not likely to be a potential source of energy because there are very few sites around the world which are suitable for building tidal barrages, and the rise and fall of sea-water during high and low tides is not enough to generate electricity on a large scale.

Write two forms in which solar energy manifests itself in sea.

Two forms in which solar energy manifests in the sea:-

(i) Sea-waves energy.
(ii) Ocean thermal energy.

Compare and contrast biomass and hydroelectricity as sources of energy.

(i) Biomass is a renewable source of energy and hydroelectricity is also a renewable source of energy.
(ii) The use of biomass by burning causes air pollution but the use of hydroelectricity does not cause any pollution.
(iii) Biomass gives heat energy which can be used for cooking and heating only. On the other hand, hydroelectricity can run all types of electrical appliances.
(iv) Biomass energy can be obtained without using any special device but hydroelectricity can be produced only by establishing hydro-power plants.

(a) What is geothermal energy's ?
(b) What is the source of heat contained in geothermal energy ?
(c) Explain how, geothermal energy is used to generate electricity.
(d) State two advantages of geothermal energy.
(e) State two disadvantages of geothermal energy.

(a) Geothermal energy is the heat energy from hot rocks present inside the earth.
(b) Hot rocks present inside the earth are the source of heat contained in geothermal energy.
(c) Extremely hot rocks present below the surface of earth heat the underground water and turn it into steam. As more and more steam is formed between the rocks, it gets compressed to high pressures. This high pressure steam is brought up through pipes and is used to run the turbine of a generator to produce electricity.
(d) Advantage of geothermal energy.
(i) It is very economical to use.
(ii) It does not cause any pollution.
(e) Disadvantage of geo thermal energy
(i) It is not available everywhere.
(ii) Deep drilling in the earth is required, which is technically very difficult and expensive.

What are the limitations of energy that can be harnessed from the sea ?

Limitations of energy that can be harnessed from the sea:
1. There are very few sites around the world that are suitable for building tidal barrages for harnessing tidal energy. Moreover, the rise and fall of seawater during high and low tides is not enough to generate electricity on a large scale.
2. The harnessing of sea-waves energy is a viable proposition only at those places where sea waves are very strong.
3. Though the energy potential from the sea is very large but its large-scale exploitation is difficult at the moment because of the huge cost required in the infrastructure.

State two ways in which the energy of sea-waves can be harnessed.

Sea-waves energy can be harnessed by the following ways:

Wave Energy: the kinetic energy possessed by huge waves near the seashore can be trapped to generate electricity. Their kinetic energy can be used to rotate turbines which will eventually produce electricity.
Tidal Energy: Due to the gravitational pull of mainly the moon on the spinning earth, the level of water in the sea rises and falls. The difference in sea-levels gives us tidal energy. Tidal energy is harnessed by constructing a dam across a narrow opening to the sea. A turbine fixed at the opening of the dam converts tidal energy to electricity.

(a) What is biogas ? Name the major component of biogas.
(b) What are the raw materials used for making biogas ?
(c) Describe the construction and working of a biogas plant with the help of a labelled diagram.
(d) Write any two uses of biogas.
(e) Write any two advantages of using biogas. Solution :

(a) Biogas is a mixture of gases produced by anaerobic degradation of biomass in the presence of water but in the absence of oxygen. Methane is the major component of biogas.
(b) Cow-dung and water.
(c) Construction and working of biogas plant: img
A biogas plant consists of a wall-shaped, underground tank called digester, which is made of bricks, and has a dome shaped roof D. The dome acts as a gas-holder. There is a gas outlet S at the top of the dome having a valve V. There is a sloping inlet chamber I connected to a mixing tank M and a rectangular outlet chamber O connected to the over flow tank F.
Cow dung and water are mixed in equal proportions in the mixing tank M to prepare the slurry. This slurry is fed into the digester tank through the inlet chamber Ito fill the tank upto the cylindrical level. Then, the cow-dung undergoes anaerobic degradation with the evolution of biogas which collects in the dome. The pressure of biogas on the slurry forces the spent slurry to go into the overflow tank F through outlet chamber O. from where it is removed.
(d) Two uses of biogas:
(i) For cooking purpose
(ii) For lightning purpose
(e) Two advantages of biogas:
(i) Smoke-free cooking
(ii) High calorific value
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(a) What are the advantages of nuclear energy ?
(b) State the disadvantages of nuclear energy.

(a) Advantages of nuclear energy
(i) It produces a large amount of useful energy from a very small amount of a nuclear fuel.
(ii) Once the nuclear fuel is loaded into the reactor, the nuclear power plant can go on producing electricity for two to three years at a stretch. There is no need of feeding the fuel again and again.
(iii) It does not produce gases like $$CO_2$$ or $$SO_2$$.
(b) Disadvantages of nuclear energy
(i) The waste products of nuclear fission reactions are radioactive which keep on emitting harmful radiations for thousands of years and are difficult to store or dispose safely.
(ii) Very high cost of installation is required.
(iii) There is a limited availability of uranium fuel.

Why are Thermal Power Stations usually located near a river?

Thermal power stations use steam to generate electricity and river contain ample amount of water which reduce the cost of transportation of water to the plant. River water is also used for cooling spent steam to condense it back into hot water for making fresh steam.

What are the various factors which we should keep in mind while choosing a source of energy.

Various factors to be kept in mind while choosing a source of energy are:
1. the ease of extracting energy from that source
2. the cost of extracting energy from that source
3. the efficiency of technology available for extracting energy from that source
4. the damage to environment caused by using that source

What are the advantages and disadvantages of using nuclear fuel for generating electricity?

Advantages of using nuclear fuel Electricity can be produced for almost two to three years with the same uranium fuel in a nuclear power plant. Disadvantages of using nuclear fuel: The nuclear wastes produced by the fission of uranium-235 during the generation of electricity are radioactive and extremely harmful.

When the rnaterial A mined from the earth is heated strongly in an insufficeint supply of air, it produces a solid fuel B which consists mainly of carbon. When another material C obtained from trees is heated in an insufficient supply of air, it produces another solid fuel D which also consists mainly of carbon. Name A, B, C and D.

A is coal; B is coke; C is wood; D is charcoal.

(a) What is the source of energy of the sun and other stars ?
(b) Describe the working of a hydrogen bomb.
(c) What is common between the sun and a hydrogen bomb ?

(a) Nuclear fusion reaction of hydrogen is the main source of energy of the sun and other stars.
(b) The hydrogen bomb consists of heavy isotopes of hydrogen (deuterium and tritium) along with lithium-6. The explosion of hydrogen bomb is done by using an atom bomb. When the aton bomb is exploded, its fission reaction produces a lot of heat which raises the temperature of deuterium and tritium to $$107^oC $$ in a few microseconds. Then fusion reactions of deuterium and tritium take place producing a tremendous amount of energy. This explodes the hydrogen bomb. Lithium-6 is used to produce more tritium needed for fusion.
(c) The common thing between the sun and hydrogen bomb is that the source of energy is same for both the sun and the hydrogen atom, i.e. nuclear fusion.

(a) Differentiate between nuclear fission and nuclear fusion.
(b) Which of the two, nuclear fission and nuclear fusion, is made use of :
(i) for the production of electricity ?
(ii) for making a hydrogen bomb ?
(c) Which produces more energy : nuclear fusion or nuclear fission ?
(d) Calculate the energy released in joules when 5 g of a material is completely convened into energy during a nuclear reaction.
(e) How much is this energy in MeV ?
(Speed of light $$= 3 \times 10^8 m/s$$)

	Nuclear Fission	Nuclear Fission
Fusion Natural occurrence of the process:	Fission reaction does not normally occur in nature.	Fusion occurs In stars. stch as the sun.
Byproducts of the reaction:	Fission produces many highly radioactive particles.	Few radioactive particles are produced by fusion reaction, but if a fission 'trigger is used radioactive particles will resat from that.
Energy Ratics:	The energy released by fission is a million times greater than that released In cherrical reactions: but lower than the energy released by nuclear fusion.	The energy released by fusion is three to four times greater than the energy released by fission.
Nuclear weapon:	One class of nuclear weapon is a fission bomb. also known m an atomic bomb co atom bomb.	One dass of nuclear weapon Is the hydrogen bomb. which uses a fission reaction to 'trigger' a fusion reaction.
Energy requirement:	Takes little energy to split two atoms in a fission reaction.	Extremely high energy Is required to be ng two or more protons dose enough that nuclear forces overcome their electrostatic repulsio.

(b) (i) Nuclear fission
(ii) Nuclear fusion
(c) Nuclear fusion
(d) Mass $$m-5_g =.00\,5kg$$. Speed of light. $$c= 3\times 10^8 \,m/s$$
We know that $$E =mc^2$$
$$ E= 0.005\times (3\times 10^8)^2$$
$$E=4.5\times 10^{14} J$$
(e) $$ 1 MeV = 1.602 \times 10^{-13} J$$
$$ 1 J = \dfrac {1}{1.602 \times 110^{-13}}MeV$$
$$4/.5 \times 10^{14} J = \dfrac {4.5 \times 10^{14}}{1.602 \times 110^{-13}} = 2.808 \times 10^{27}MeV$$

A certain form of energy is available due to the difference in the temperature of water at the surface of the ocean and its deeper levels.
(a) Name the form of energy.
(b) Is this energy ultimately derived from the sun or not ?
(c) Explain how this form of energy can be converted into electricity.
(d) What is the minimum temperature difference in water at the surface of ocean and its deeper level which is required to operate power plants based on this energy ?

(a) Ocean thermal energy
(b) No
(c) Ocean thermal energy is used to generate electricity in an Ocean Thermal Energy Conversion power plant (OTEC power plant). A temperature difference of $$20^o C$$ or more between the surface water and deeper water is needed for the operation of these plants. The warm surface water of ocean is used to boil a liquid like ammonia or chlorofluorocarbon. The high pressure of liquid vapours is used to turn the turbine of a generator and produce electricity.
(d) $$20^o C$$.

Can any source of energy be pollution-free? Explain your answer with an example.

No source of energy can be pollution-free. Exploiting any source of energy disturbs the environment in some way or the other. In any given situation, the source we would choose depends on factors such as the ease of extracting energy from that source, the economics of extracting energy from the source, the efficiency of the technology available, and the environmental damage that will be caused by using that source.

In some cases, the actual operation of a device like the solar cell may be pollution-free, but the assembly of the device would have caused some environmental damage.

What are the environmental consequences of the increasing demand for energy ?

The environmental consequences of the increasing demand for energy are:
(i) The combustion of fossil fuels is producing acid rain and damaging plants, soil, and aquatic life.
(ii) The combustion of fossil fuels is increasing the greenhouse effect.
(iii) Nuclear power plants are increasing radioactivity in the environment.
(iv) Construction of hydro-power plants is disturbing the ecological balance.

List any four areas where solar cells are being used as a source of energy.

Solar cells are used for many scientific and technological applications.

$$i.$$ Artificial satellites and space probes like Mars orbiters use solar cells as the main source of energy.

$$ii.$$ Radio or wireless transmission systems or TV relay stations in remote locations use solar cell panels.

$$iii.$$ Traffic signals, calculators, and many toys are fitted with solar cells.

$$iv.$$ The solar cell panels are mounted on specially designed inclined roof tops so that more solar energy is incident over it.

State one limitation of solar energy available from solar cells.

Solar energy is a very good and renewable source of energy has sonic disadvantages also.

1. Solar cells and their installation require a lot of money and therefore not many people can afford it.

2. Also they are weather dependent and cannot be used in the rainy season or at the time of the year when the sun is not visible.

Name the three forms in which energy from oceans is made available for use. What are OTEC power plants? How do they operate?

The three forms in which mercy from oceans is made available for use are-
1) Wave energy
2) Tidal energy
3) Thermal energy
OTEC stands for - Ocean Thermal Energy Conversion Plant.
Water present at the surface of the sea is continuously being heated due to sunlight but. The water present in the deep-sea level is quite cold because sunlight is unable to penetrate deep into the water. So, this difference in the different levels of water in the sea can be utilized efficiently to create electricity. It is done in OTEC i.e. ocean thermal energy conversion plants.

What is the minimum wind velocity required to obtain useful energy with a windmill?

A windmill is a device (mill) that converts wind energy into electricity by using the blades of the windmill. The minimum velocity required by a windmill to obtain useful energy is $$1.5$$ kilometers per hour.
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What normally drives the alternators in a Thermal Power Station? What fuels can be used to heat water in the boiler?

Generally, the alternators in a Thermal Power Station are driven by the power of high pressure steam.
To heat water in the boiler, fuels like coal or natural gas can be used. The water on heating produces steam whose pressure rotates the steam turbines.
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Draw a labelled diagram of floating gas holder type biogas plant and describe it's working. Mention any two advantage of using animal dung for making biogas over using It as a fuel in the form of dried dung cakes.

Biogas plant has a dome-shaped digestor in which cow dung is kept. It is completely isolated and thus does not have oxygen in them. In this anaerobic conditions. methanogens (methane producing bacteria) perform their function $$\&$$ produces methane $$(CH_4)$$ by digesting the cow dung. Along with methane, carbon-dioxide $$(CO_2)$$. hydrogen sulphide $$(H_2S)$$ is also produced. These gases so produced is recovered from the gas outlet while the remaining slurry can be rued as fertilizer.
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Which part of the solar energy is responsible for heating the surfaces ?

The solar energy coming from the sun is basically electromagnetic radiation that is produced on the surface of the sun.

This solar energy basically comprises of the infrared radiations, the visible light, and ultraviolet radiation. The infrared radiations are lower frequency radiations than the visible spectrum while the ultraviolet is the radiations that have frequencies higher than the visible spectrum. The infrared radiations are basically related to heat and are responsible for heating surfaces.

What are the criteria you would consider when trying to categorize something like a good fuel?

Criteria: The Fuel should be:

1. High Energy - yield.

- It should have high calorific value and burn to produce a maximum output of heat. It should also have a normal ignition temperature.

2. Easily available.

- It should be available in abundance. The resource should be accessible or easy to produce.

3. Environmental friendly.

- It should leave no residue or produce greenhouse gases on burning like an eco-friendly or clean fuel.

4. Easily transportable.

- It should be easy to transport.

5. Low Cost.

- It should be economical. It should be cheap for regular use.

6. Storable.

- It should be easy to store.

Which power plant works on earth's gravity ?

Hydropower plant works on earth gravity.

Explanation:

There is an opening in the dam that uses gravity to drop water down a pipe called a penstock. The moving water causes the turbine to spin, which causes magnets inside a generator to rotate and create electricity.

List in tabular form two distinguishing features of a thermal power plant and a geothermal power plant.

	Thermal power plant:	Geothermal power plant:
Source	Burning of fossil fuels in the power stations to produce steam, which further runs the turbine.	The 'hotspots', areas where molten rocks formed in the earth's crust are pushed up because of geological changes and trapped. When underground water comes in contact with this hotspot, steam is produced This steam is routed through a pipe to a turbine and generate electricity.
Commercial utilization	Transmission of electricity more efficient than transporting coal and petroleum over the same distance, hence located near oil fields.	The cost of production would not be much, but very few commercially viable sites
	They are called thermal power plants as heat energy is converted into electrical energy	Sometimes hot water from that region finds an outlet to the surface, such areas are known as hot springs.

The increase in demand for energy is affecting our enviroment adversely. List two such effects.

1- High energy demand, leads to a high carbon footprint.

Overusing electrical energy can cause a bump in the amount of greenhouses gases, which enter the atmosphere. Like leaving on your charger even after the phone has been charged.

This is like using up the resources by wasting them.

2- It leads to unfavorable climatic conditions like air pollution.

By looking at the use of coal energy. During its combustion, other gases are also released into the air. These gases concentrate the air and cause pollution.

Name the energy obtained from sea or ocean water due to the difference in temperature at the surface and in deeper sections of these water bodies.

Ocean Thermal Energy.

Explanation:

The ocean thermal energy is obtained from the sea or ocean due to the difference in temperature between the surface water and the water below. This happens because the water on the surface gets heated due to the exposure to sunlight, while the lower surfaces of water are comparatively colder.

Name the largest component of bio-gas.

Methane is the largest component of bio-gas.

Detail :

Biogas is produced by anaerobic digestion or fermentation of biodegradable materials such as biomass, manure, sewage, municipal waste, green waste, plant material, and energy crops. This type of biogas comprises primarily methane.

It is advantageous to convert bio-mass into a bio-gas rather than burning bio-mass directly. Why?

Yes, It is advantageous to convert biomass into biogas rather than burning biomass directly. The reasons are:

Bioenergy is energy derived using organic material, especially plant matter, as fuel. The material burned or processed to produce bioenergy (the "feedstock") is called biomass.

Biomass has been an energy source for as long as humans have used wood fires to warm themselves and cook food. Wood is still the most commonly used biomass fuel. Some great advantages are:

It is an excellent fuel, which is 75% methane.

It burns without smoke.

It leaves no residue like ash in wood, charcoal, and coal burning.

At the same time, it also has a high heating capacity.

In some developing countries, crop and logging residues, and a dried mixture of straw and animal dung are also common biomass fuels.

The slurry left behind is used as a manure.

Unlike most other sources of energy, biomass is a potentially renewable resource. By definition, bioenergy sources also include coal, petroleum, and natural gas, because these fossil fuels are derived from ancient plant biomass laid down in early geologic ages. However, these are non-renewable sources of energy and by convention are omitted when discussing bioenergy.

The big advantage of bioenergy is that its use reduces the use of such non-renewable energy sources.

Biomass contains stored energy. Justify it.

Biomass contains stored energy as:

(i) Biomass (animal and plant products) is used to form biogas.

(ii) Biomass does not have a good heating capacity, it produces a lot of smoke
Cow dung, various plant materials like residue after harvesting the crops, vegetable waste, and sewage are decomposed in the absence of oxygen to give biogas.
Biogas is stored, and drawn through pipes for use.
It is excellent fuel, gaseous state, non-polluting, and high heating capacity.
The slurry left behind can be used as manure, rich in nitrogen and phosphorus.

How does the burning of fossil fuels cause air and soil pollution?

Burning of fossil fuels causes air and soil pollution by the following means:

1. Fossil fuel is a non-renewable source of energy, and it contains carbon particles and when they are burnt, they release carbon monoxide, which is a poisonous, colorless compound, and when it is inhaled it reduces the oxygen-carrying capacity of the blood.

2. The air becomes polluted and when clouds forms in the presence of these polluted air, it falls down as acid rain which is very much dangerous and disrupts the soil fertility and destroys the crop.

The above-mentioned points signify that the burning of fossil fuel not only causes air pollution but also it causes soil pollution.

State the meaning of the term "hot spot" in the context of the earth's crust. Write one advantage and one limitation of utilizing energy obtained from the hot spots.

Hotspot is a region, where molten rock is trapped. It is formed in the deeper hot regions of Earth’s crust, and is pushed upwards through geological changes.

When underground water comes in contact with hotspots, steam is generated. This steam is trapped and routed through a pipe to a turbine and is used to generate electricity.

Sometimes hot water from that region also finds an outlet. It is known as hot springs.

Advantage: The cost of production of electricity is not much.

Disadvantage: There are very few such commercially viable sites, where energy can be exploited.

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The slippery surface between colliding tectonic plates resulted in a huge release of energy into the sea and this resulted in a massive tsunami. The 2011 devastating tsunami rolled over many parts of Japan and caused huge damages. The disaster also caused the three reactors at Fukushima nuclear power plant to melt down which released dangerous harmful radiation into the surrounding areas and led to a national power shortage.
(a) What could be the reason for damage to nuclear reactors?
(b) How did it affect the environment and the people?
(c) Do you think nuclear energy is a future source of energy?

a) The reason for damage to nuclear reactors: Nuclear reactors are not environment friendly. They use uranium and plutonium in the reactors. These elements when exposed due to a meltdown will cause harmful radiation which could cause many diseases including cancer and other genetic disorders. A tsunami was once such a natural calamity that damaged the nuclear reactor in Fukushima.

b) Nuclear reactors contain radioactive material. The radiation from these materials is hazardous. They may affect the genetic materials in the cell which can be passed to subsequent generations in the form of incurable diseases. Radioactive waste if not disposed of properly can cause harm to the environment as well as human beings.

c) No, I do not think nuclear energy is a future source of energy as many countries have decided to shut down their nuclear power plants.

Explain why only a small part of the solar energy that strikes the upper regions of atmosphere reaches the surface of the Earth.

When the solar energy falls on the top surface of the atmosphere then the following happens:

(i) Some solar energy is reflected back into space by the atmosphere, and

(ii) The atmosphere also absorbs a lot of solar energy. for example. most of the ultraviolet rays are absorbed by the ozone layer.

So. the solar energy which reaches us through the Earth's atmosphere is mainly in the form of heat rays (infrared rays) and visible light. which is a small part of solar energy.

Mention any two disadvantages of producing hydroelectricity by building dams on rivers.

Disadvantages:

(i) A vast variety of flora and fauna (plants and animals) get affected.

(ii) Dams can be constructed only at a limited number of places.

Give some advantages of solar energy.

Solar power is pollution free and causes no greenhouse gases to be emitted after installation.
Reduced dependence on foreign oil and fossil fuels.
Renewable clean power that is available every day of the year, even cloudy days produce some power.
Return on investment unlike paying for utility bills.

Mention any two advantages of producing hydroelectricity by building dams on rivers.

The advantages of producing hydroelectricity by building dams on rivers are as follows:

(i) The generation of electricity from water does not produce any environmental pollution.

(ii) Water energy is a renewable source of electric energy which will never get exhausted.

What is meant by a wind energy farm? Write one of its practical applications. Give any three limitations of using wind energy farms.

A wind energy farm is a place where there are provisions to harness the energy of wind using windmills in large numbers. Such farms are put up in places, where the wind blows throughout the year, in the required amount.

The practical application of a windmill farm is that the energy output of each windmill in the farm is coupled together to get electricity at a commercial scale.

Limitations of using a wind energy farm:

i. Wind energy farms can be established only in those areas where the wind blows for a greater part of the year.

ii. Wind speed should be higher than $$15 \ km/hr$$ to maintain the speed of the turbine.

iii. There should be some backup facilities like storage cells, to take care of energy needs during a period when there is no wind.

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What energy transformation occur in a hydro power plant?

A hydro power plant converts potential energy into kinetic and kinetic into electrical energy.

State two advantages and two disadvantages of geothermal energy.

Advantages:

(i) The use of geothermal energy does not cause any pollution.

(ii) The use of geothermal energy is quite economical.

Disadvantages:

(i) It is not available everywhere.

(ii) Deep drilling in the Earth to obtain geothermal energy is very difficult.

How are the tidal energy, wave energy, and ocean thermal energy different from each other?

The source of tidal energy is tides, the rise, and fall in the level of the sea, produced by the gravitational pull of the moon, on the spinning earth. It is an intermittent source of energy.

The source of wave energy is the kinetic energy of waves. The wave energy is also an intermittent source of energy.

The source of ocean thermal energy is the difference in temperature of the water, at the surface, and in the deeper sections. Unlike wave and tidal energies, the ocean thermal energy is fairly constant.

Also, unlike thermal energy, the electricity conversion of both tidal and wave energy usually involves mechanical devices.

Though wood is a renewable source of energy, but the use of wood as a fuel is not a wise decision. Explain.

Wood is a renewable source of energy. It is obtained by cutting trees. A new plant sapling usually takes more than 15 years to grow and mature into a tree. Therefore, replenishment of cut down trees takes a very long time. Cutting down of trees causes depletion of the forests leading to imbalance in nature. Due to unsuitable air and the above reasons, usage of wood as a source of energy is not a wise decision.

What are the environmental consequences of using fossil fuels?

Fossil fuels have the following environmental effects:
(i) Air pollution:
Burning of fossil fuels release oxides and sulphides in the air and many other harmful gases like carbon monoxide, sulphur dioxide, etc. These cause various health problems and also lead to acid rain which further affects water and soil resources.

(ii) Greenhouse effect:
On burning fossil fuels, a large amount of carbon dioxide is released into the atmosphere. this is a greenhouse gas and does not allow the sun rays reflected from the earth surface to escape into the atmosphere. Thus, increasing the temperature of the atmosphere. This is called greenhouse effect and results in global warming.

State the important uses of wind energy.

The wind energy is used:

(i) To generate electricity.

(ii) To grind the wheat in flour mills.

(iii) To run a pump to draw water from the ground.

Explain the principle of working of a windmill.

A windmill converts wind energy into rotational energy by means of its blades. The basic principle of every windmill is to convert the kinetic energy of wind into mechanical energy which is used to rotate the turbine of an electrical generator to produce electricity.

Describe how electric energy is generated in hydro power plants.

(i) A high rise dam is constructed at a suitable place on the river to obstruct the flow of water and thereby. collect water in larger reservoirs. Due to rise in water level the kinetic energy of flowing water is transformed into potential energy of stored water

(ii) The water from the high level in the dam is carried through sluice gates and pipes to the turbine of electric generator, which is fitted at the bottom of the dam. Due to flowing water, turbine is rotated at a fast rate and hydel electricity is produced.

(iii) A hydro power plant converts the potential energy of falling. stored water into electricity.

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In a school, there are seventy teachers and most of them have their personal vehicles. There are many teachers who come from the same place but everyone prefers coming by their personal vehicle. On the other hand, the students of the school either come by buses or by carpooling. Whose practice of commuting to school is nature friendly? Justify your answer.

The students way of commuting is nature friendly because they are saving fossil fuels, which are non-renewable sources of energy, and by this practice also reducing pollution.

Which part of the solar cooker is responsible for greenhouse effect?

The glass sheet in the solar cooker creates a greenhouse effect. Glass sheet has a property that allows the infra-red rays of shorter wavelength from the Sun to get in the device but does not allow the infra-red rays of longer wavelength to leave the solar heating device. Therefore. heat energy is trapped inside the heating device.

Give an example of indirect harnessing of solar energy.

All green plants prepare carbohydrates from carbon dioxide and water in the presence of sunlight by the process of photosynthesis. All non-green plants and animals directly or indirectly consume food from the green plants (producers) and store this food in their bodies in the form of chemical energy. In other words. solar energy is transformed into chemical energy.

What is the importance of hydro power plants in India?

Importance: Hydro power plants are of prime importance as about $$25$$ per cent of our energy requirement in India is met by hydro power plants. India as a rising developing country should depend more on clean and green renewable sources of energy. Since the water in the reservoir would be refilled each time it rains (hydro power is a renewable source of energy) there is no worry about hydro electricity sources getting used up the way fossil fuels would get finished one day.

Write the advantages of solar cells.

Solar cells create savings in electricity.
It is a renewable source of energy.
It is an environmentally friendly energy. No pollution occurs.

State two characteristics which a source of energy must have.

The two characteristics that a source of energy must have are as follows :
1. It should be such that it can provide a sufficient amount of useful energy at a steady rate over a long period of time
2. It should be safe and convenient to use, economical and easy to store and transport.

Why is there a need for harnessing non conventional sources of energy?

$$\text{Following are the main reasons: because of which there is a need to harness non- conventional sources of energy}$$:

(a) $$\text{Non-renewable fuels}$$: Fossil fuels are the main energy sources for us. But it takes millions of years for the formation of fossil fuel. The rate at which we are using them means they are not going to last many years from now. They would be definitely exhausted sooner rather than later.
(b) $$\text{Polluting fuels}$$: Burning of fossil fuels releases oxides of carbon, nitrogen and sulphur. These are polluting gases. Carbon dioxide is a greenhouse gas. Carbon monoxide can be poisonous even in low concentration, Oxides of Sulphur and nitrogen cause acid rain. Air pollution also results in increased cases of respiratory problems.

What is biomass? What can be done to obtain bio-energy using biomass?

Biomass is a fuel that is obtained from organic materials. It is a renewable and sustainable source of energy. Following are some methods of harnessing biomass:
(a) Using firewood as fuel
(b) Using cow dung cakes as fuel
(c) Production of gobar gas

Why is there a need to harness non conventional sources of energy? Give two main reasons.

Two reasons for the need to harness non conventional sources of energy are as follows:
(a) Conventional sources are going to be exhausted in near future.
(b) Burning of fossil fuels causes environmental pollution.

What are the environmental consequences of using fossil fuels?

Environmental consequences of using fossil fuels are as follows:

(a) Increased level of carbon dioxide is resulting in global warming. Global warming is causing drastic changes in weather patterns across the globe.

(b) Oxides of Sulphur and nitrogen cause acid rain. Acid rain is harmful for building and monuments and also for living beings.

(c) Increase in air pollution is causing more cases of respiratory diseases.
(d) Smog is a major problem in cities because it reduces visibility. It creates a problem for pilots and drivers.

Give a brief description of harnessing on non conventional source of energy.

Tidal energy is non conventional energy.

$$\text{Methods to Harness Tidal Energy:}$$

For this, a cylindrical structure is vertically placed in coastal areas where tides come.
A turbine is fitted at the top of this cylinder.
When the tide comes, air gushes through the cylinder. This turns the turbine and electricity is generated.
When the tide goes, air moves in opposite direction. This also turns the turbine and electricity is generated.

What is geo-thermal energy? Explain in brief.

$$Geo-thermal\ energy$$ - It is the heat energy possessed by rocks inside earth and is harnessed to produce electricity. Deep inside the earth, hot rock are present at the hot spots, which are responsible to heat up the underground water causing it to turn the steam, which is compressed between rocks at higher pressure. Drilling of holes deep until the hot spots for extraction of steam through the pipes causes the turbines to rotate that are connected to the armature of an electric generator in order to produce electricity.
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Write any two hazards of nuclear power generation.

Two hazardous of nuclear power generation are:
Contamination: Improper nuclear-waste storage and disposal result in environmental contamination
High cost of installation: Nuclear power plant needs a lot of money for their set up. Moreover the limited availability of uranium adds to the disadvantage.

State two advantages and two disadvantages of producing hydro-electricity.

The two advantages of producing hydro-electricity are:
1. It is a renewable source of energy.
2. Does not cause any environmental pollution.
Two disadvantages of producing hydro-electricity are:
1. Animal and plant life gets destructed due to the construction of dams over the water bodies.
2. Due to this process the ecological balance in the downstream areas of water bodies such as rivers is disturbed.

State the energy transformation in the following:
Electricity is obtained from wind energy

A windmill consists of a fan-like structure erected on a strong standing support at a considerable height. The strong wind moves the wings of the windmill and this turns the turbines of the electric generator which produces electricity. Thus the mechanical energy of wind is converted to electrical energy.

What is solar energy? How is solar energy used to generate electricity in a solar power plant?

1. $$Solar$$ energy is the energy obtained from the $$Sun$$.

2. By using solar cells, solar energy is converted into electricity. A typical cell develops a voltage of $$0.5–1 \ V$$ and can produce about $$0.7 \ W$$ of electricity when exposed to the Sun.

A large number of solar cells are, combined in an arrangement called solar cell panel that can deliver enough electricity for practical use.
On commercial scale, these solar cell panels are further combined in a solar power plant.
The silicon used in solar cells absorbs the solar energy to generate a potential difference voltage across the positive and negative ends of the solar cell.
This voltage makes the solar cell behave as a source of electricity just like a dry cell.

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State two advantages and two limitations of using wind energy for generating electricity.

Two advantages of using wind energy for generating electricity :
1. It is a renewable source of energy.
2. Does not cause any kind of pollution.

Two limitations of using wind energy for generating electricity:
1. To establish wind farms, a large area of land is required.
2. Establishment of the wind farm is expensive.

State the energy transformation in the following:
Electricity is obtained from hydro electricity

In hydropower plant , water is allowed to fall from large heights on the blades of a turbine.The falling water rotates the turbine and turbine rotates the generator attached to it.And this generator generates electricity when rotating.

So Mechanical energy of falling water is converted into Electcrical energy.

What results in the increase of carbon dioxide contents of earth's atmosphere?

The increase of the carbon dioxide content in the earth's atmosphere can be contributed to industrial growth, deforestation and burning of fossil fuels.

State four ways for the judicious use of energy.

The four ways with which energy can be used judiciously are :
1.Fossil fuels should be used for limited purposes when no other alternative source of energy is available .
2.Energy wastage should be avoided .
3.The practice of chopping down trees must be banned. More trees must be planted .
4.Efforts should be made to utilize energy in groups/ community .

What is wind energy? How is wind energy used to produce electricity? How much electric power is generated in India using wind energy?

Wind energy is the kinetic energy of the large masses of air in motion.
Wind energy is used in the form of a wind generator to generate electricity by utilizing a windmill to drive the wind generator.

Wind power accounts nearly 8.6% of India's total installed power generation capacity and generated 28,604 million Kwh (MU) in the fiscal year 2015-16 which is nearly 2.5% of total electricity generation.

What is hydro energy? Explain the principle of generating electricity from hydro energy. How much hydro electric power is generated in India?

1.Hydro energy is the kinetic energy possessed by flowing water.
2.Principle of generating electricity from hydro energy- water flowing from higher altitudes is accumulated at a dam placed at height. This water is made to fall on water turbine that is positioned near the base of the dam. The shaft of the turbine is in contact with the armature of a dynamo or an electric generator. The turbine is set in motion and so is the dynamo and due to electromagnetic induction electricity is produced.
3.Approximately $$14\%$$ of the total electricity is generated by the hydro electricity in India .

What is tidal energy? Explain in brief.

The energy obtained from the rise and fall of tides is called tidal energy.

Tidal barrages or dams are constructed across a narrow opening to the sea. Water rushes into the dam when the sea level rises. This moves the blades of the turbines which are attached at the opening of the dam. This results in the generation of electricity.

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Explain the difference.
Conventional and Non-conventional Sources of energy.

	Conventional Source of energy	Non- conventional sources of energy
	1. Conventional sources of energy are the sources that are commonly in use since long time.	1. Non- conventional sources of energy refers to the sources that are identified few decades ago
	2. They can be exhausted due to over consumption .	2. They cannot be exhausted.
	3. They pollute the environment on a large scale and adds to global warming.	3. They are environment friendly sources , which do not cause pollution.
	4. They are primarily used for industrial and commercial purposes.	4. They are mainly used for domestic purposes.
	5. It is costly	5. Comparatively less expensive
	Example: Coal , natural gas , water, firewood	Example: Solar energy, wind energy, tidal energy

Give an example to explain that the use of modern eco-friendly technologies is more efficient and less polluting.

Modern eco-friendly technologies are most efficient and less polluting. Modern energy-efficient appliances such as refrigerators, ovens, freezers, dishwashers, etc. Make use of significantly less energy than the older appliances. They are star rated in accordance to their efficient use of electricity. The more the star rating, the higher is the efficiency.

State two advantages and two disadvantages of using wind energy for generating electricity.

$$\underline{\text{Advantages of using wind energy:}}$$
1. It does not cause any kind of pollution.
2. It is an everlasting source.
$$\underline{\text{Disadvantages of using wind energy:}}$$
1. The establishment of a windmill is fruitful only in those areas where wind blow is appreciable.
2. A large area of land is needed for the establishment of a wind farm.

What is hydro energy? Explain the principle of generating electricity from hydro energy. How much hydroelectric power is generated in India?

The kinetic energy of flowing water or the potential energy of water at a height is a source of hydro energy. Hydro power plants convert the potential energy of falling water into electricity.

Principle of a hydroelectric power plant is that the water flowing in high altitude rivers is collected in a high dam (or reservoir). The water from dam is then allowed to fall on a water turbine which is located near the bottom of the dam. The shaft of the turbine is connected to the armature of an electric generator or dynamo.

At present only $$23$$% of the total electricity is generated by the hydroelectric power plants.

What is wind energy? How is wind energy used to produce electricity?

Wind energy is an important source of renewable energy. The landmass and water bodies by solar radiation generate air movement and cause winds to blow. This kinetic energy of the wind can be used to do work.

A windmill essentially consists of a structure similar to a large electric fan that is erected at some height on a rigid support. To generate electricity, the rotatory motion of the windmill is used to turn the turbine of the electric generator. The output of a single windmill is quite small and cannot be used for commercial purposes. Therefore, a number of windmills are erected over a large area, which is known as wind energy farms. The energy output of each windmill in a farm is coupled together to get electricity on a commercial scale.

How does proper insulation of home save energy ?

It is possible to maintain a comfortable temperature inside by properly insulating a home. It will reduce the cost of heating devices in winter and cooling devices in summer.

What social initiatives must be taken for the sensitive use of energy ?

Listed below are the social initiatives that must be taken:
$$\cdot$$ Community involvement will be effective in reducing the misuse of electricity
$$\cdot$$ Non-government organizations (NGO's) can be used to create social awareness of the sensitive use of resources.
$$\cdot$$ Public awareness can be improved through mass media and children's participation in campaigns and eco-club activities.

Remake the table taking into account relation between entries in three columns.
I II III
Coal Potential Energy Wind electricity plant
Uranium Kinetic Energy Hydro electric plant
Water Reservoir Nuclear Energy Thermal plant
Wind Thermal Energy Nuclear power plant

I II III

Coal Thermal Energy Thermal Plant

Uranium Nuclear Energy Nuclear Power plant

Water Reservoir Potential Energy Hydroelectric plant

Wind Kinetic Energy Wind electricity plant

State two advantage and two disadvantages of producing hydroelectricity.

Advantages of producing the hydroelectricity:
1. It does not produce any environmental pollution.
2. It is a renewable source of energy.
Disadvantages of producing hydroelectricity:
1. Due to the construction of dams over the rivers, plants and animals of that place get destroyed or killed.
2. The ecological balance in the downstream areas of rivers gets disturbed.

Which fuel is used in thermal power plant? What are the problems associated with this type of power generation?

Coal is used in thermal power plant. Problems associated with this type of power generation are:

Air pollution caused due to burning of coal: Burning of coal emits gases like carbon dioxide, sulphur oxide and nitrogen oxide which are harmful to living beings
Release of soot particles in the environment: Along with the gases released due to burning of coal, soot particles are released in the environment which can cause fatal respiratory problems.
Coal is non-renewable source of energy. So, this method of power generation will put a limit on the availability of coal in future.

Explain the difference .
Thermal electricity generation and solar thermal electricity generation.

Thermal electricity generation and solar thermal electricity generation.

$$\text{Thermal electricity generation}$$	$$\text{Solar thermal electricity generation.}$$
It uses non-renewable source of energy for electricity generation such as fossil fuels, natural gas or nuclear fuels.	It uses renewable source of energy i.e., Solar energy for electricity generation.
This method of electricity generation is not environment friendly. It causes air and soil pollution.	This is environment friendly method of electricity generation. It does not cause air or soil pollution.
This method requires maintenance.	This method does not requires maintenance.

How is electricity produced in hydro power plant?

In hydro power plant water is stored at large heights in dam which is allowed to fall on the propellers of a turbine and the falling water rotates the turbine of the generator and the generator generates electricity.

What do you understand by electrical energy? How is electricity obtained from thermal power plant?

The energy in a charged object is called electric energy. In a thermal power plant, fuel is burnt to convert water into steam. The steam is then channelized to propellers of turbine, The flow of steam facilitates the movement in turbine.And the turbine rotates the generator and it generates electricity. While doing so, kinetic energy of turbine is converted into electric energy with the help of a generator.

Give your opinion about whether hydro electric plants are environment friendly or not?

No waste products and harmful gases are released in water bodies and atmosphere when power is generated using hydroelectric power plants. Also, water is available in plenty on Earth and is renewable. Hence, there is no fear of this energy source dying out. Thus, it has no harmful effects on the environment and hence is environment friendly.

Explain with diagram step-by-step on the energy conversion in a Hydroelectric power plant.

In hydroelectric power plants, the potential energy in water stored in the dam is converted into kinetic energy of water. Fast flowing water is brought from the dam to the turbine at the bottom of the dam. The kinetic energy of the flowing water drives the turbine. The turbine in turn drives the generator to generate electricity.

Potential energy in water $$ \rightarrow $$ Kinetic energy in flowing water $$ \rightarrow $$ Kinetic energy in turbine $$ \rightarrow $$ Electrical energy

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Give scientific reason
The construction of the turbine is different for different types of power plants.

The construction of the turbine is different for different types of power plants. This depends on the type of energy source used for driving the turbine. Like in thermal power plants, the steam turbine is used whereas in hydro-power plants, water turbine is used.

What is electric energy? How is electricity produced in following:
(a) Hydel electric plant
(b) Wind energy plant
(c) Solar energy plant

Electrical energy is the amount of work done or energy consumed in a given amount of time.

(a) Flow of water is used for moving the turbine. Turbine converts kinetic energy into electric energy.

(b) Blades of windmill move due to wind speed. Fan of windmill is attached to a turbine. Turbine converts kinetic energy into electric energy.

(c) Solar energy plant uses two methods to produce electricity. In one method, photovoltaic cells convert heat energy into electric energy. In another method, water is converted into steam by using heat energy. Steam is then utilized to turn the turbines and electricity is produced.

What is biomass energy? What are its uses?

The excreta of animals, cow dug, wild plants, and dry leaves of plants are fermented in a digestive tank. The produced gas is called biogas/Gobar gas which is known as bio mass-energy. This gas bums with a smokeless flame. Therefore it is a non-polluting gas. This is used as a house fuel and for lighting the house.

What is a source of energy?

A source of energy is one which is capable of providing an adequate amount of useful energy.

Write down the advantages and limitations of solar cooker.

$$Advantages$$:

• Eco-friendliness
• Maintain better air quality indoors, reduce carbon monoxide emissions
• Less expensive
• Don't cause any environmental pollution

$$ Limitation: $$

• Cooking with solar cookers obviously requires sunlight, which makes it difficult to use during winter months and on rainy days.
• Cooking also takes a significantly longer time compared to conventional methods.
• Solar cookers are not as efficient at retaining heat as conventional cooking devices. Factors such as wind, rain, and snow can seriously hinder operation, and in such weather conditions, even after the food is cooked, it will lose its warmth very quickly.

We get different forms of energy from the Sun. Attempts are underway now to utilize solar energy to its maximum. What are the devices used for this?

Solar power is energy from the sun that is converted into thermal or electrical energy. Solar technologies can harness this energy for a variety of uses, including generating electricity, providing light or a comfortable interior environment, and heating water for domestic, commercial, or industrial use.

Various instruments used for harnessing solar energy are:

• Solar panel
• Solar water heater
• Solar cooker
• Solar thermal power plant

What are the disadvantages of fossil fuels?

The oxides of carbon, nitrogen and sulphur that are released on burning fossil fuels are acidic oxides. These lead to acid rain which affects our water and soil resources. In addition to the problem of air pollution, greenhouse effect of gases like carbon dioxide etc. These are the disadvantages of fossilic fuels

It is said that energy can neither be created nor destroyed; then how does energy crisis occur?

Law of conservation of energy states that energy can neither be created nor be destroyed. But there are losses of energy and that occurs during the transfer or conversion process of energy. There are renewable sources as well as non-renewable sources of energy and crises occur when there is finishing of non-renewable sources of energy which are limited in number.

Explain the working of a hydroelectric power plant to produce electricity.

In order to produce hydroelectricity, high rise dams are constructed on the river to obstruct the flow of water and thereby collect water in very large reservoirs. The water from high level in the dam is carried through pipes, to the turbine, at the bottom of the dam. The turbines are connected to the generator. Rotation of the turbines makes the generator produce electricity. Water when stored at a height in the dam has a large amount of potential energy which gets converted into the kinetic energy of flowing water when it is allowed to fall on the turbines it gets converted into mechanical energy of the turbine and finally gets converted into the electric energy by the generator

Kerala has a long coastal land. Still, ocean is not considered as a major source of energy. Why?

In Kerala usually, waves are low. So they have less energy. Also during the tides of Kerala sea coasts, the sea attitude does not increasingly rise. Due to this, the ocean is not considered the major source of energy for Kerala.

Write down the name of some power stations in Kerala.

Some power stations in Kerala are :

$$\cdot$$ ldukki - Moolamattom.

$$\cdot$$ ldukki - Pallivasal.

$$\cdot$$ Alappuzha - Kayamkulam.

Why is it said that geothermal power plants are not possible in Kerala? Discuss and record.

There are some minor environmental is-sues associated with geothermal power. Geothermal power plants can in extreme cases cause earthquakes. There are heavy upfront costs associated with both geothermal power plants and geothermal heating/cooling systems. Very location-specific (most resources are simply not cost-competitive). Some countries have been blessed with great resources - Iceland and Philippines meet nearly one-third of their electricity demand with geothermal energy. If geothermal energy is transported long distances by the means of hot water (not electricity), significant energy losses has to be taken into account. Geothermal power is only sustainable (renewable) if the reservoirs are properly managed.

Solar energy has an incredible future in the field of transportation. We are in its infant stage. Write an essay on the topic "Prospects of solar energy.

Solar energy is the ultimate energy source. All energy sources are related and connected with solar energy in one or the other way. The principal advantages associated with solar cells are that they have no moving parts, require little maintenance and work quite satisfactorily without the use of any focussing device. Another advantage is that they can be used in remote and inaccessible hamlets or very sparsely inhabited areas in which laying of a fuel station may be expensive and not commercially viable. So the electrical energy from the solar cells can be used to drive electric vehicles in such remote areas.

Artificial satellites and space probes like Mars orbiters already use solar cells as the main source of energy.

Explain how solar energy is stored in various forms on earth's ecosystem.

Sun is the major source of energy available in earth, during photosynthesis the light energy is converted into chemical energy and is stored in plant cells. Since this plant reaches in animals as food, the stored energy reaches in animals too. And when these animals die.The remains of the animals burried in earth transforms under high pressure and temperature and becomes fuels. In this way solar energy transforms and gets stored in different bodies in different forms.

Visit a hydroelectric power station and try to understand different stages of the production of electricity. Make use of this principle and find out the scope of mini hydroelectric power project.

There are only some primary expenses to build a hydrogen-electric power station. Hydroelectric power stations must be constructed only in areas of heavy rainfall and good streamflow. If these required conditions are satisfied, the production of electricity from such power station is very profitable one.
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Visit a biogas plant and explore the possibility of establishing a community biogas plant in your region.

A biogas plant is where biogas is produced by fermenting biomass. The substrate used for the production of this methane-containing gas usually consists of energy crops such as corn, or waste materials such as manure or food waste.

Generally, the biomass required to construct a biogas plant may not be available from a single house and it is not profitable to construct separate biogas plant for each house. We know that the social cleanliness is equally important as personal cleanliness, due to several reasons, like.economic advantages, it is necessary to run a social community biogas plant, where the bio materials required can be gathered from individual houses and collected.This will make the plant economical as the cost will be shared by every house.

Compare biomass and biogas.

Biogas: Biogas refers to a mixture of different gases produced by the breakdown of organic mater in the absence of oxygen.

Biomass: Since fuels like fire-wood and cow-dung cakes are plant and animal products, the source of these fuels is said to be bio-mass.

What will you call the nuclear reaction in which small atoms combine?

Nuclear fusion is the process by which two or more atomic nuclei join together, or “fuse,” to form a single heavier nucleus.

How are fossil fuels formed?

After millions of years underground, the compounds that makeup plankton and plants turn into fossil fuels. Plankton decomposes into natural gas and oil, while plants become coal. Today, humans extract these resources through coal mining and the drilling of oil and gas wells on land and offshore.

Watch the animation video of nuclear fission and fusion
Which nuclear reaction happens in an atom bomb?

$$Nuclear \, fission $$

Nuclear fission produces the atomic bomb, a weapon of mass destruction that uses power released by the splitting of atomic nuclei. When a single free neutron strikes the nucleus of an atom of radioactive material like uranium or plutonium, it knocks two or three more neutrons free.

Identify the relation and fill in the blanks.
Hydrogen bomb: Nuclear fusion :Atom bomb:______

$$Nuclear \, fission $$

Atomic bombs rely on fission, or atom-splitting, just as nuclear power plants do. The hydrogen bomb, also called the thermonuclear bomb, uses fusion, or atomic nuclei coming together, to produce explosive energy. Stars also produce energy through fusion.

A man pointing at a car running on petrol says. 'This car is running on solar energy. Write down your responses about this matter.

We use fossil fuels like petrol or diesel in cars. The plants which lived millions of year ago have also used solar energy for photosynthesis to make food. Humans and animals grew up by taking these plants and fruits. Then this humans and animals are burned in earth after their death and became fossil fuels. Fuels are formed out of them. This fuel is being used in cars so the ultimate source of energy here is the solar energy itself. The vehicles connected with solar panels uses solar energy in the direct form.

Coal is the most abundant fossil fuel on the earth.
How did the fossil fuels originate?

Fossil fuel originates from plants and animals that went under the earth many years ago changed into fossil fuels by undergoing changes under high pressure, high temperature, and absence of oxygen.

Various situations which use solar energy are given in the diagram. What are the advantages & disadvantages of solar energy list them?

Advantages:

Renewable Energy Source.

Low Maintenance Costs.

Reduces Electricity Bills.

Disadvantages:

Solar Energy Storage Is Expensive.

Weather-Dependent.

Costs are very high.

A B
(1) Uses the energy of water stored at a height. (a) Pallivasal Power Station.
(2) Uses the heat generated by the burning of fuels. (b) Ramagundam Power Station.
(3) Uses nuclear energy. (c) Kalpaklcam Power Station.
Names of power stations and statements related to them are given below in two groups. Match them suitably.

a - 1,
b - 2,
c - 3

Pallivasal Hydroelectric Project is located around 8 km from the town of Munnar of Idukki in Kerala. The power project is commissioned in 1940 with an installed capacity of 37.5 Megawatt. ... The power station is owned by the State Government of Kerala and its operations were conducted by Kerala State Electricity Board.

NTPC Ramagundam, a part of National Thermal Power Corporation, is a 2,600 megawatt (MW) Power station situated at Ramagundam in Peddapalli district in Telangana, India. It is the current largest power station in South India. It is the first ISO 14001 certified "Super Thermal Power Station" in India.

Madras Atomic Power Station located at Kalpakkam about 80 kilometers south of Chennai, India, is comprehensive nuclear power production, fuel reprocessing, and waste treatment facility that includes plutonium fuel fabrication for fast breeder reactors.

Using the relation from the first pair, complete the other.
Hydroelectric power station - flowing water
Thermal power station -

Hydroelectric power station- flowing water

High speed flowing water falls on turbine to rotates it and produce electricity.

Thermal power station - Steam at high pressure and temperature.

High speed steam at high pressure and temperature strikes with turbine to rotates it and produce electricity.

Compare Nuclear fission and Nuclear Fusion.

$$\underline{\text{Nuclear fusion:}}$$ The process in which lighter nuclei are combined to form heavier ones.

$$\underline{\text{Nuclear Fission:}}$$ The process by which the nuclei of greater mass are split into lighter nuclei, using neutrons. The mass of small nuclei is less than that of the parent nucleus.

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Why it is called as fossil fuels?

Complete the table.
Powerhouse Class Source of energy
Moolamatam (a) water from dams
Pallivasal (b) (c)
Kayamkulam (d) Naphtha
Neyveli (e) (f)

a. Hydroelectric power station.

b. Hydroelectric power station.

c. Water from dams.

d. Thermal power station.

e. Thermal power station

f. Lignite.

Using the relation from the first pair, complete the other.
Moolamattom - Hydroelectric power station
Rawatbhata -

Moolamattom - Hydroelectric power station

Rawatbhata - Nuclear power station

Moolamattom Power Station — Moolamattom Power Station is the biggest underground hydroelectric project in India.

The Rajasthan Atomic Power Station is located at Rawatbhata in the state of Rajasthan, India.

Kuttiadi, Kayamkulam, kaiga, kalpakkam, Mooiamattom
Some power stations in India shown in above.
Tabulate the above power stations according to the energy changes.

Hydroelectric power station	Thermal power station	Nuclear power station
Kuttiadi Mooiamattom	Kayamkulam	Kaiga Kalpakkam

Kuttiadi, Kayamkulam, kaiga, kalpakkam, Mooiamattom
Some power stations in India shown in above.
Industrially electricity produced in the form of a.c. Why ?

It helps the transformer for rising and decreasing voltage.

Write any three disadvantages associated with hydro power plant.

Disadvantages of Hydroelectric Power :

Hydroelectric power is generated only near the rivers having water throughout the year. This electric power has to be carried to the substations for distribution to the houses and factories situated far off from the sites of hydroelectric power stations. This is done through the transmission wires, so a lot of money is to be spent on this process.
A large area of fertile land is submerged at the site of the dam constructed for tapping energy from the flowing water.
A large number of people residing near the site of a dam are dislocated. So, a lot of problems are to be faced in rehabilitating this population. That is why there is a lot of opposition by the people around the site of the dam for the construction of the dam.
A large number of plants and wildlife in the area of the dam are submerged in water. So, a large variety of flora (plants) and fauna (animals) is destroyed.
Hydroelectric dams cannot be constructed everywhere. They are constructed mostly in a hilly areas.

Solar cooker takes more time as compared to the LPG to boil potato or rice, yet Kunal uses solar cooker for such type of cooking:
(i) Why does Kunal uses solar cooker instead of LPG? Give reasons for your answer.
(ii) Name the phenomenon which is responsible for obtaining high temperature in solar cooker.

(a) Kunal uses solar cooker instead of LPG because:

There are no energy losses while cooking on the solar cooker as the food gets cooked in a controlled environment whereas cooking on the LPG leads to maximum percentage of energy loss. Also, LPG is a non-renewable source of energy.
Temperature controlled cooking retains the nutrient value of the food.
Using the solar cooker, LPG can be saved which result reduction in the emission of $$CO_2$$ as there is no combustion of a fuel during the usage of solar cooker.

CO2
(b) Greenhouse effect is name of the phenomenon which is responsible for obtaining high temperature in solar cooker. The transparent glass sheet over the cooker is responsible for the greenhouse effect in a solar cooker. Infrared radiation emitted by sunlight is trapped in the solar cooker and used in heating it up.

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List reasons why we need to look for alternate sources of energy.
Or
Why is there a need to harness non-conventional sources of energy ? Give two main reasons.

To fulfill the requirement of increasing demand of energy.
To ease out the pressure on the conventional sources of energy.
To reduce the pollution caused by the use of conventional sources of energy.

Name the part of a biogas plant where reactions take place in the absence of oxygen.

A digester chamber is the part of a biogas plant where reactions take place in the absence of oxygen.
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Biogas is considered to be a boon to the farmers. Give reasons.
Or
List any three reasons due to which bio-gas is considered to be an excellent fuel.

Bio-gas is pollution free.
It is cheap as raw material {i.e., cow dung and waste of plants and vegetables) to produce biogas is available free of cost to the farmers.
The remains or used slurry in a bio gas plant is used as manure by the famers in the field to get good yields of crops.

Kuttiadi, Kayamkulam, kaiga, kalpakkam, Mooiamattom
Some power stations in India shown in above.
How does the electricity produced from Moolamattam power station ?

Water stored at a height is allowed to flow down a penstock pipe. The energy of flowing water is used to rotate the turbine and generate electricity.

Define tidal energy. Explain how the tidal energy is harnessed and write one limitation of the use of tidal energy.

Tidal energy: The energy produced by the surge of ocean water during high and low tides due to difference in sea-levels is called tidal energy. The high and low tides occur due to the gravitational pull of the moon. This causes enormous movement of water.
Tidal energy is harnessed by constructing a dam near the shores. During the high tides waterflows into the dam and during the low tides, water flows out. This flowing water rotates the turbine, present at the opening of the dam and produces electricity.

Bio gas is an excellent fuel. Justify the statement by giving two reasons. Mention the main constituents of bio gas along with its percentage.

Biogas is an excellent fuel because:

$$(i)$$ It burns without smoke, leaves no residue like ash in wood, charcoal, and coal burning.

$$(ii)$$ Its heating capacity is high.

The main constituents of biogas is methane $$(75 \%)$$.

Out of two elements A and B with mass number $$2$$ and $$235$$ respectively, which one is suitable for making ,
(a) a nuclear reactor,
(b) a hydrogen bomb?
Name the nuclear reaction involved in each case. Write one difference between the two types of nuclear reactions.

(a) For a nuclear reactor - element B with mass number

235235 is suitable as a fuel in a nuclear reactor.
(b) For a hydrogen bomb - element A with mass number

22 is suitable for making the hydrogen bomb.
The nuclear reaction involved in
(a) nuclear reactor is nuclear fission reaction and
(b) nuclear bomb is nuclear fusion reaction.
Difference between fission and fusion:
Fusion reaction releases much greater energy with non-radioactive products than the energy released in fission reaction with radioactive products.

Name two sources of energy which are pollution free.

The sun, wind and water are the sources of energy which are pollution free.

Out of two solar cookers, one was covered with a plane glass slab and the other was left open. Which of the two solar cookers will be more efficient and why?

The solar cooker which was covered with a plane glass slab would be more efficient. The glass lid allows the heat radiation from sun to enter the solar cooker but does not allow the reflected heat radiation to escape or go outside the box. Thus, heat trapped inside the box increases the temperature. Glass lid also reduces heat loss due to reflection.

Why are fossil fuels known as a non-renewable source of energy?

Fossil fuels like coal, petroleum, and natural gases take millions of years for their formation. If these fuels are exhausted today, then they will not be formed very soon. Hence, they are known as non-renewable sources of energy.

Write the name of the substance whose vapours are used to run the turbine of the generator of ocean thermal energy plant.

Ammonia is the name of the substance whose vapours are used to run the turbine of the generator of ocean thermal energy plant

Mention the minimum temperature difference required between surface water and water at a depth of up to $$2$$ km in an ocean thermal energy plant.

Energy from the sun heats the surface water of the ocean. In tropical regions, surface water can be much warmer than deep water. This temperature difference can be used to produce electricity and to desalinate ocean water.

$$20^o$$$$C$$ is the minimum temperature difference required between surface water and water at a depth of up to 2 km in an ocean thermal energy plant.

Mention any three qualities of an ideal source of energy.

A good source of energy should have the following characteristics. It should:

supply enough amount of useful energy.
be easily stored.
economical.

Name two activities in our daily life in which solar energy is used.

For cooking food using solar cookers.
For drying clothes and food grains.

Name two renewable or non-conventional sources of energy.

Following are two renewable or non-conventional sources of energy:

Solar energy
Energy from the sea

Name any two elements that are used in fabricating solar cells.

Silver and Silicon are the two elements that are used in fabricating solar cells.

What steps can be taken to minimize environmental pollution caused by the burning of fossil fuels ?

We can minimize environmental pollution caused by the burning of fossil fuel by

growing more and more trees,
Using smokeless chulahs and
smokeless chimneys in thermal power plants.

Answer the following question in short and to the point.
Write the names of the two dams of Gujarat. How are dams useful to society?

Two dams of Gujarat are:-

1. Statue of Unity

2. Dharoi Dam

A dam is a barrier that stops or restricts the flow of water or underground streams. Reservoirs created by damns not only suppress floods but also provide water for activities such as irrigation , human consumption , industrial use, aquaculture and navigability.

What is the main basic cause for winds to blow ?

The most basic cause for winds to blow is the existence of a pressure difference between two locations on the earth. A wind is nothing but movement of gases from one place to another. So when there is a low pressure area the gases from high pressure area move to occupy that area and hence the wind blows.

The pressure of a region where maximum sunlight falls decreases as compared to the region where minimum sunlight falls.The reason being air on heating expands and pressure decreases.And relatively cold air contracts and has large pressure. The air moves from a region of high pressure (i.e., cold region) to the region of low pressure (i.e., hot region). This moving air is the wind.

The figure indicates the fission reaction of a heavy nucleus of Uranium.
a. Write down an activity to make energy available by using lighter nucleii.
b. Calculate the energy obtained if $$1 \ g$$ matter changes into energy during nuclear fission reaction ($$c=3 \times 10^8 \ m/s$$).
c. What will be the result if the reaction shown in the above figure continues?
d. Why are we establishing nuclear reactors despite of the realisation that nuclear reactors are controlled nuclear bombs?

a. Nuclear fusion is a reaction in which two or more atomic nuclei are combined to form one or more different atomic nuclei and subatomic particles (neutrons or protons).
b. $$E = mc^2$$

Given:

$$m = 1 \ g= \dfrac{1}{1000} \ kg$$

$$E=\dfrac{1}{1000}\times (3 \times 10^8) \times (3 \times 10^8)$$

$$=\dfrac{9 \times 10^{16}}{10^3}= 9 \times 10^{13} \ J$$

c. Continuous fission reaction ends in an explosion (atom bomb).

d. Energy crisis and industrial growth promote production of energy. So we are establishing nuclear reactors even though they are quite risky. However, numerous safety precautions are taken while handling such radioactive materials used in the reactors as they have a health hazard.

What is hydro energy ? Explain the principle of generating electricity from hydro energy.
How much hydro electric power is generated in india ?

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Explain the principle and working of a biogas plant using a labeled diagram.

The arrangement of producing biogas from animals dung, human excreta, industrial and domestic wastes is known as a biogas plant.
Fixed-dome type biogas plant:
Construction: Fixeddome type biogas plant
It consists of a well-like underground tank made of bricks and cement. This tank is called a digester and has inlet and outlet valves. The roof of the tank is dome-shaped. A gas outlet pipe at the top of the dome is fitted. The dome of the digester acts as a storage tank of biogas. There is a mixing tank made above the ground level which is connected to the inlet valve of the digester through a slopping inlet chamber below the ground level. On the other side of the digester, a rectangular tank called an outlet chamber is constructed with bricks and cement. This outlet chamber is connected to the overflow tank which collects the used slurry.
Working: Animals-dung is mixed with water to make a slurry in the mixing tank. This slurry enters the digester through the inlet chamber. The digester is filled partially with slurry so that enough space is left above it in the dome for the collection of biogas. The slurry in the digester is left for about two months for fermentation. Anaerobic microorganisms are responsible for this action. As a result of fermentation, biogas is formed which is collected in the dome. When a sufficient amount of biogas is collected in the dome, it exerts a large pressure on the slurry and forced it to go into the overflow tank through the outlet chamber. The biogas is taken out from the dome through a pipe and used for cooking food or heating water whenever required. Once the biogas plant starts functioning, more and more slurry may be fed into the digester to get the continuous supply of biogas. The used slurry collected in the overflow tank is rich in nitrogen and phosphorus which are essential for the growth of crops and plants. Hence this used slurry can be used as manure.
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I	II	III
Coal	Potential Energy	Wind electricity plant
Uranium	Kinetic Energy	Hydro electric plant
Water Reservoir	Nuclear Energy	Thermal plant
Wind	Thermal Energy	Nuclear power plant

A	B
(1) Uses the energy of water stored at a height.	(a) Pallivasal Power Station.
(2) Uses the heat generated by the burning of fuels.	(b) Ramagundam Power Station.
(3) Uses nuclear energy.	(c) Kalpaklcam Power Station.

Powerhouse	Class	Source of energy
Moolamatam	(a)	water from dams
Pallivasal	(b)	(c)
Kayamkulam	(d)	Naphtha
Neyveli	(e)	(f)

Sources Of Energy - Class 10 Physics - Extra Questions