Some Natural Phenomena - Class 8 Physics - Extra Questions

Lightning is an electric discharge. Within a thundercloud way up in the sky, many small bits of ice (frozen raindrops) bump into each other as they move around in the air. All of those collisions create an electric charge. After a while, the whole cloud fills up with electrical charges. The positive charges or protons form at the top of the cloud and the negative charges or electrons form at the bottom of the cloud. Since opposites attract, that causes a positive charge to build up on the ground beneath the cloud. The electrical charge at ground concentrates around anything that sticks up, such as mountains, people, or single trees. The charge coming up from these points eventually connects with a charge reaching down from the clouds to the nearest point from the sky and lightning strikes. As tall buildings are closer to the sky, they strike on high rise buildings.
Hence, the statement is true.

During the development of a thunderstorm, the air currents move upward while the water droplets move downward. These vigorous movements cause separation of charges. By a process, the positive charges collect near the upper edges of the clouds and the negative charges accumulate near the lower edges. There is accumulation of positive charges near the ground also. When the magnitude of the accumulated charges becomes very large, the air which is normally a poor conductor of electricity, is no longer able to resist their flow. Negative and positive charges meet, producing streaks of bright light and sound. We see streaks as lightning. The process is called an electric discharge.
The process of electric discharge can occur between two or more clouds, or between clouds and the earth. In a situation where a man is taking bath outdoors during a thunderstorm, as water is a very good conductor of charges, it will conduct the electric charges to the human body and cause destruction.
Hence the statement is true and entry is 1.

Below are measures to protect ourselves from lightning.

(1) If you hear thunder, rush to a safer place like a house or a building. If you are travelling by car or by bus, you are safe inside with windows and doors of the vehicle shut.
(2) Lightning can strike telephone cords, electrical wires and metal pipes. During a thunderstorm contact with these should be avoided.
(3) Bathing should be avoided during thunderstorms to avoid contact with running water.

Some of the measures to protect ourselves from lightning are as follows:
(i) We should stay in a completely closed place. 

Human body is a conductor of electricity. So, when we touch a charged object, our body conducts its charges to the Earth. That is why a charged body loses its charge, if we touch it with our hand. This phenomenon is known as earthing.

If we are outside and an earthquake strikes, we should take the following precautions:
(i) We should try to find an open field away from tall buildings, installations, tall trees, and electric wires and poles.
(ii) If travelling in a bus or a car, we should not come out when an earthquake strikes and go to an open field.

A person struck by lightning should be made to lie in a place where there is good air circulation. In order to prevent blood clotting keep the body warm by massaging. Give artificial respiration and press strongly on the chest to maintain heartbeat and the person must be taken to a hospital immediately.

Earthquakes are caused by tectonic movements in the Earth's crust. The main cause is that when tectonic plates collide, one rides over the other, causing orogeny (mountain building), earthquakes and volcanoes. The boundaries between moving plates form the largest fault surfaces on Earth.

Earthquakes are usually caused when rock underground suddenly breaks along a fault. This sudden release of energy causes the seismic waves that make the ground shake. When two blocks of rock or two plates are rubbing against each other, they stick a little. When the rocks break, the earthquake occurs.

Earthquakes can be extremely violent or so slight that they only register on instruments. They are caused by sudden movements of the Earth's tectonic plates. The study of earthquakes is called seismology. ... The magnitude of an earthquake, and the intensity of shaking, is usually reported on the Richter scale.

Lightning conductor will not work, if left hanging in the air because in order to work, it must be connected to the ground by using any metal (copper) plate, so that the charge can pass through it to the ground.

Lightning happens when the negative charges (electrons) in the bottom of the cloud are attracted to the positive charges (protons) in the ground.

During the development of a thunderstorm, the air currents move upward while the water droplets move downward. These vigorous movements cause separation of charges. By this process, the positive charges collect near the upper edges of the clouds and the negative charges accumulate near the lower edges. There is accumulation of positive charges near the ground also. When the magnitude of the accumulated charges becomes very large, the air which is normally a poor conductor of electricity, is no longer able to resist their flow. Negative and positive charges meet, producing streaks of bright light and sound. We see streaks as lightning. The process is called an electric discharge.
The process of electric discharge can occur between two or more clouds, or between clouds and the earth. 
Hence, the statement is false and entry is 0.

A is the lightning conductor and B is the copper plate. 

When both the straws are rubbed with a dry cotton cloth, they will acquire the similar charge and hence they will repel each other.

Lightning is an electrical discharge. During lightning atmospheric electric charge may discharge through landline telephone wires and may become dangerous. Therefore it is safer to use a wireless telephone instead of a landline telephone during lightning.

If you are outside, then the precautions that can be taken are :

Lightning is an electric current. Within a thundercloud way up in the sky, many small bits of ice (frozen raindrops) bump into each other as they move around in the air. All of those collisions create an electric charge. After a while, the whole cloud fills up with electrical charges. The positive charges or protons form at the top of the cloud and the negative charges or electrons form at the bottom of the cloud. Since opposites attract, that causes a positive charge to build up on the ground beneath the cloud. The grounds electrical charge concentrates around anything that sticks up, such as mountains, people, or single trees. The charge coming up from these points eventually connects with a charge reaching down from the clouds and lightning strikes.
Therefore, Lightning is caused due to discharge of oppositely charged clouds.

A lightning rod or lightning conductor is a metal rod or metallic object mounted on top of an elevated structure, such as a building, a ship, or even a tree, electrically bonded using a wire or electrical conductor to interface with ground or earth through an electrode, engineered to protect the structure in the event of lightning strike. 
If lightning hits the structure, it will preferentially strike the rod and be conducted to ground through the wire, instead of passing through the structure, where it could start a fire or cause electrocution. Lightning rods are also called finials, air terminals or strike termination devices.
In a lightning protection system, a lightning rod is a single component of the system. The lightning rod requires a connection to earth to perform its protective function. 

Lightning is an electric current. Within a thundercloud way up in the sky, many small bits of ice (frozen raindrops) bump into each other as they move around in the air. All of those collisions create an electric charge. After a while, the whole cloud fills up with electrical charges. The positive charges or protons form at the top of the cloud and the negative charges or electrons form at the bottom of the cloud. Since opposites attract, that causes a positive charge to build up on the ground beneath the cloud. The grounds electrical charge concentrates around anything that sticks up, such as mountains, people, or single trees. The charge coming up from these points eventually connects with a charge reaching down from the clouds to the nearest point from the sky and lightning strikes. As tall buildings are closer to the sky, they strike on high rise buildings.

They repel each other because the glass rod and the fur both are positively charged and like charges repel each other.

An electroscope is an instrument used to find out whether a body is charged or not.

On rubbing ebonite rod with fur, the ebonite rod gains electrons and so gets negatively charged while fur loses some electrons and so gets positively charged.

Earthquakes can also be caused by underground nuclear explosions or eruption of a volcano or when a meteor hits the earth.

By performing mouth to mouth breathing. A lightning victim does not carry any electrical charge and so cannot electrocute the person giving him first aid.

No, we should not carry an umbrella in a thunderstorm because thunderstorms are generally accompanied by lightning. Electric discharge from the clouds can travel through the metallic rod of the umbrella during lightning. This may give an electric shock to the person who is carrying it. Hence, it is not safe to carry an umbrella during lightning.

An electroscope is used to detect whether a body is charged or not. It consists of a metal rod. At one end of the rod, two leaves of aluminium foil are fixed and at the other end, there is a metal disc. The leaves of aluminium foil are placed inside a conical flask and the flask is corked to isolate the leaves from air.
When the metal disc is touched with a charged body, the aluminium strips move away from each other. Some of the charges of the body are transferred to the strips through the metal rod. Nature of charges on both the leaves and the charged body are the similar. Hence, both the leaves of the aluminium foil will move away from each other. If the body was not charged, then the leaves of the foil would remain as they were before. They would not repel each other.

a) When the straw is rubbed by a piece of paper it acquires charge. When brought near the suspended straw, the suspended straw which was electrically neutral , derives an induced opposite charge on the surface and gets attracted by the charged end of the other straw and moves toward it. The force acting between these straws is the electrostatic force.

Electric field inside the conductor is always zero i.e a conductor acts as a shield for the objects placed inside it and prevents it from the effect of external electric field. That's why it is safer to be inside the car as the metal surface of the car acts as a shield for the person and so prevents the person fron lightening.

Positive lighting is particularly dangerous because it frequently strikes away from the rain core$$,$$ either ahead or behind the thunderstorm$$.$$ It can strikes as far as $$5$$ or $$10$$ miles $$(8$$ or $$16$$ kilometres$$)$$ from the storm$$,$$ in areas that most people do not consider to be a lighting-risk area$$.$$  

The free electrons are transferred from one body to another on rubbing thus making one body negatively charged $$($$one which accepts electrons$$)$$ and the other becomes positively charged $$($$one which donates electrons$$).$$  

The positive charges collect near the upper edges of the clouds and the negative charges accumulate near the lower edges. There is an accumulation of positive charges near the ground also. When the magnitude of the accumulated charges becomes very large, the air which is normally a poor conductor of electricity is no longer able to resist their flow. Negative and positive charges meet, producing streaks of bright light and sound. We see streaks as lightning. The process is called an electric discharge.

Lightning is an electric discharge from cloud which can travel through metallic rod of the umbrella because metal is a very good conductor of electricity. Because of this, the person carrying umbrella may experience electric shock. Hence it is not safe to raise an umbrella during thunderstorm where as umbrella made of bamboo frame are safe because bamboos are not conducting elements.

Causes of Earthquake $$\rightarrow$$ Earthquakes are caused by sudden tectonic movements in the Earth's crust. The main cause is that when tectonic plates, one rides over the other, causing orogeny collide (mountain building), earthquakes. The largest fault surfaces on Earth are formed due to boundaries between moving plates.

The main cause of earthquake is volcanic eruptions. Such type of earthquakes occurs in areas, with frequent volcanic activities. When boiling lava tries to break through the surface of the earth, with the increased pressure of gases, certain movements are caused in earth's crust

In seismology$$,$$ a seismic zone is an area of seismicity potentially sharing a common cause$$.$$ A type of seismic zone is a wadati$$-$$Benioff zone which corresponds with the down$$-$$going slab in a subduction zone$$.$$

$$Electroscope$$$$:-$$ Electroscope is used to detect and measure electric charges$$.$$

The lighting conductor provides a very low resistance path between the top of the lighting conductor rod via a substantial strip of metal to the ground so that the current as a result of a lighting strike does not flow through the building to which is attached$$.$$

During thunderstorms, lightning and thunder go hand in hand. In fact, thunder is heard as a direct result of lightning. When the charged layers of clouds get discharged, the sparks are seen as lightning and heard as thunder.

$$Lightning\,\,conductor:-$$ A metal road that is placed on a building and connected with the ground below to protect the building from being damaged by lightning$$.$$

Lightning Conductor is a device used to protect buildings from the effect of lightning. A metallic rod, taller than the building, is installed in the walls of the building during its construction. One end of the rod is kept out in the air and the other is buried deep in the ground. The rod provides easy route for the transfer of electric charge to the ground. The process is called earthing. 

When the cork bits touch the rod, they share the charge of the rod of the same sign and so get strongly repelled away.

The positive charges collect near the upper edges of the clouds and the negative charges accumulate near the lower edges. There is an accumulation of positive charges near the ground also. When the magnitude of the accumulated charges becomes very large, the air which is normally a poor conductor of electricity is no longer able to resist their flow. Negative and positive charges meet, producing streaks of bright light and sound. We see streaks as lightning. The process is called an electric discharge.

$$Earthquake:$$ 

The moving blades of ceiling fans, get charged due to friction between air and the blades. The charged surface of the blades attract dust particles from the air which keep accumulating on the surface.

Lightning conductors have a pointed end which has a very small surface area. The smaller surface area ends (spikes) attract charges from the atmosphere easily. When a charged cloud passes over a lightning conductor, an opposite charge is induced in the pointed end. This charged end will have a very high charge density which can attract the lightning easily preventing it from striking any other part of the building.

It is due to the electrostatic force between the balloon and the wall. Opposite charges attract each other.

Take a positively charged pith ball electroscope. Bring the charged body near the pith ball (without touching it). if the pith ball moves away, the body has a similar charge (positive charge) and if the pith ball moves towards the body, the body has a negative charge.

Both ebonite rods are rubbed fur with have similar charge(-ve charge). We know like charges repel each other.
$$ \therefore $$ Rods repel each other.

When an ebonite rod is rubbed with fur, the electrons are transferred from fur to the ebonite rod. Ebonite now has an excess of electrons and is negatively charged and fur due to the deficit of a same number of electrons gets a positive charge.

An ebonite rod when rubbed with fur acquires the negative charge.

A glass rod rubbed with silk is suspended near an ebonite rod rubbed with fur. A glass rod rubbed with silk will be positively charged. An ebonite rod rubbed with fur will be negatively charged. The glass rod and the ebonite rod will attract each other because like charges repel and unlike charges attract

Both objects before rubbing are neutral.
On rubbing transfer of electrons from one object to another object take place.
The body from which electrons are transferred gets deficient in electrons and becomes positively charged.
The body to which electrons are transferred has excess electrons and becomes negatively charged.

Frictional electricity is the electricity produced by rubbing two suitable bodies and the transfer of electrons from one body to other. The body which loses the electrons becomes positively charged while the body which receives the electrons, becomes negatively charged.

Place copper sheet around the leaves of an electroscope. Touch the nob with a charged, body. Opposite charge is formed on the leaves. Opposite charge of it is formed inside the sheet and the same charge is formed outer surface of the sheet. Now the sheet is earthed, the charge on outer surface will be disappeared.

The body of car is metallic. it provides electrostatic shielding to the person in the car because electric field inside car is zero. the discharging due to lightning passes to the ground through the metallic body of the car.

In tall modern buildings, there are plenty of metal rods inside the concrete work, connecting from the top to bottom of the building and to the earth. Electric charge from the lightning clouds, reaching the building, is conducted safely to the earth through these metal rods. So the building are protected from damage due to lightning discharge.

• We will close the windows of the car and remain inside. Even in the case of a direct lightning strike, the entire charge will pass through the surface of car while shielding whatever that is inside the car.

A bolt of lighting travels at a speed of more than $$400,000 km/h$$. It can heat the air around it to a temperature which is more than 4 times of temperature of the surface of the sun. So it is very dangerous. 

The precautions taken to protect us from lightning are:

A glass rod is rubbed with silk. glass rod loses electrons and becomes positively charged.
Silk gains electrons and becomes negatively charged.
Explanation  : Suppose glass rod in neutral from has $$ 10 $$ protons and $$ 10 $$ electrons  i.e. $$ 10 $$ units of positive charge.
and $$ 10 $$ units of negative charge.
While silk has (in neutral state ) $$ 7  $$ electrons and $$ 7 $$ protons (suppose) i.e. $$ 7 $$ units of negative charge and $$ 7 $$ units of positive charge.
Suppose on rubbing together glass rod losses $$ 2 $$ electrons.
Now glass rod has $$ 8$$ electrons and $$ 10 $$ protons on it.
i.e. $$ 8 $$ units of negative charge and $$ 10 $$ units of positive charge i.e. glass rod had net $$2 $$ units of positive charge . thus , glass rod has acquired positive charge.
Silk has now $$ 9 $$ units of negative charge and $$ 7 $$ units of positive charge i.e. silk has net $$2 $$ units of negative charge. thus , silk has acquired negative charge.

An Ebonite rod is rubbed with fur.
Ebonite rod gains electrons and acquires negative charge while fur loses electrons and acquires positive charge.

If two glass rods after rubbing with silk, are hung near each other, then they repel each other, figure (a). 

Plastic strip when rubbed with dry cloth gets charged due to charging by friction. The plastic strip acquires positive charges and dry cloth acquires the negative charge.

The person standing under the tree is safer. Electric charge always get concentrated at sharp edges. So more possibility for danger due to lightning is to the man under coconut tree than the another one because coconut tree has sharp edges.

Electrons have been removed from the glass object. Negative charge has been removed from the initially neutral rod, resulting in a net positive charge on the rod. The protons cannot be removed from the rod; protons are not mobile because they are within the nuclei of the atoms of the rod.

When both balloons are rubbed with a cloth, they acquire like charges and hence will repel each other. However, in the second case when both are rubbed with different materials, they may acquire like or unlike charges and may repel or attract

When we touch a charged body, it loses charge to the earth through our body, or in other words it gets discharged. The process of transferring of charge from a charged object to the earth is called earthing.

During thunderstorms, huge clouds are formed such that the air currents move upward while the water droplets move downward. These vigorous movements cause separation of charges. The positive charges collect near the upper edges of the clouds and the negative charges accumulate near the lower edges. When the magnitude of the accumulated charges becomes very large, the air which is normally a poor conductor of electricity, is no longer able to resist their flow. Negative and positive charges meet, producing streaks of bright light and sound. This sound is what causes thunder. Hence, Vijay is right.

If the materials used for constructing a building were good conductors, lightning can still strike the building. However, in the case of a lightning strike the inside of the building will be protected from damage. During lightning strike it is safe to stay inside cars as the passengers of the car are protected from lightning because of being shielded by the metallic frame of the car. In the same way, if the building was made of conducting material, the inside of the building will stay shielded. Thus, a lightning conductor need not be installed.

Matter consists of both positively and negatively charged particles. A material which has the same amount of positive and negative charges is electrically neutral. An object gets charged when these charged particles get transferred from one body to another leading to an excess of a certain kind of charged particles. 

Electroscope is a simple device which is used to test the presence of charge in an object.