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CBSE Questions for Class 7 Physics Heat Quiz 4 - MCQExams.com
CBSE
Class 7 Physics
Heat
Quiz 4
Good conductor of heat is
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Hydrogen
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Oxygen
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Nitrogen
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None
If we keep pop corn in a pressure cooker on a flame, heat is transferred from flame to corn by :
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Conduction
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Radiation
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Convection
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None
Explanation
The direct contact of cooker and corn is an example of conduction. The transfer of heat takes place through the metallic bottom of the pressure cooker ans reaches the corn.
Bad conductor of heat is
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Copper
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Steel
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Silver
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None of these
Explanation
Copper, steel, and silver, being metals are good conductors of heat. Non-metals are bad conductors of heat. For example,
wood, paper, air, and cloth are poor conductors of heat.
The process of transfer of heat by the movement of particles of medium from one place to another is called
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Conduction
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Radiation
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Convection
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None
Explanation
Process of heat transfer through movement of particles of medium from one place to another is convection.
Good insulator of heat is
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Wood
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Metals
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Mercury
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None
State whether given statement is True or False
Woollen yard is a bad conductor of heat.
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True
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False
Explanation
Woollen sweaters keeps us warm in winter as the air gets trapped in woollen yard. Hence the given statement is true.
A wooden rod is dipped in a cup of ice cream. The other end of the wooden rod
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becomes cold by the process of conduction
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becomes cold by the process of radiation
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becomes cold by the process of convection
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does not become cold
Explanation
Wood is a bad conductor of heat. So it will not allow conduction of heat. Therefore, the other end of the rod will remain at the same temperature.
State True or False :
Convection is not possible in vacuum.
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True
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False
Explanation
Conduction and convection are not possible in vacuum, they require medium, as in convection, heat transfer takes place only by motion of particles in the medium and in vacuum particles are not present. While radiation is possible in vacuum.
State whether given statement is True or False
Ventilation is an example of convection current in gases.
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True
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False
Explanation
Due to convection current in air, proper ventilation is maintained. The process by which impure, warm air inside a room is continuously replaced by fresh air from outside.
The water at the surface of swimming pool or lake being warmer due to
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Radiation
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Convection
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Conduction
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None
Explanation
The surface water of a swimming pool or a lake is exposed to the sun. It receives sunlight in the form of radiation. This radiation supplies heat to the surface water and hence it becomes warm.
State whether given statement is True or False
The process of convection can takes place only in liquid and gases.
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True
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False
Explanation
Convection takes place where the movement of particles of medium takes place. This is not possible in solids, it is only possible in liquid and gases.
What type of conductor should be used to make water pipes in cold countries?
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Good conductor
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Poor conductor or bad conductor
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Material does not help in such cases
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None of the above
Explanation
The materials which do not allow heat to pass through them are known as bad conductors or insulators. Poor conductors should be used to make water pipes in cold countries so that they will not allow heat to pass from water inside the pipe to the outside atmosphere to prevent water from freezing. It thus helps the pipes from bursting.
To prevent heat conduction to our hands, the handles of cooking vessels are made of bad conductors.
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True
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False
Explanation
A good conductor will transfer the heat from the vessel's handle to our hands and let our hands burn. So, a bad conductor of heat, materials are used for manufacturing of vessel's handle. The wooden handle is used as wood is a bad conductor of heat.
The temperature of a normal human being is
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$$31^{o} C$$
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$$37^{o} C$$
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$$20^{o} C$$
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$$50^{o} C$$
Explanation
$$98.4^{o} F$$ is the usual body temperature of a normal human being. It is also equal to $$37^{o} C$$.
If two bodies A and B of $$50^{0} C$$ comes in contact with each other, the heat will flow
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Body A $$\rightarrow$$ Body B
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Body B $$\rightarrow$$ Body A
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nowhere
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from both the bodies
Explanation
Heat always flows from a hot object to a cold object as shown.
Heat transfer needs a temperature difference to take place. Now here, b
oth the bodies are at the same temperature, so there will be no transfer of heat from one body to the other
If we switch on a fan heater, it blow hot air through a grille into the room, then
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Cold air rises upwards
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Hot air rises upwards
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Neither A nor B
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None
Explanation
Hot air is less dense and cold air is more dense. And we know that less dense gases rise above more dense air so hot air will rise upwards.
S.I unit of temperature is
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$$^{\circ} C$$
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$$K$$
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$$J$$
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All
Thermal radiation is also called
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infrared radiation
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EM radiation
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nuclear radiation
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None
Explanation
Thermal radiation does not include any contact between hot body and cold body. It transfers heat without any medium. It falls within infrared zone of electromagnetic radiation, so it is also called $$infrared \ radiation.$$
Find odd one out
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Copper
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Mercury
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Gold
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Wood
Explanation
Copper, mercury and gold are good conductors of heat while wood is a bad conductor.
Define insulator of heat.
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Substances through which heat can pass easily are called insulators of heat.
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Substances through which heat cannot pass easily are called insulators of heat.
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Substance which can easily freeze are called insulators of heat.
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Substances which cannot freeze easily are called insulators of heat.
Explanation
Materials which allow heat to pass through them are called conductors of heat and the material which does not allow heat to pass through them are called insulators of heat.
State True or False :
Good conductors of heat are also good conductors of electricity.
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True
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False
Explanation
Usually, good conductors of heat are also good conductors of electricity. However, this is not always true. One of the exceptions is mica. Mica is good conductor of heat but bad conductor of electricity.
Specific heat capacity is ______ for conductors of heat and _______ for insulators of heat.
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low, low
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low, high
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high, high
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high, low
Explanation
$$Q=ms\Delta T$$,
where
$$Q: \text{the amount of heat delivered to a body}$$
$$m: \text{mass of the body}$$
$$s: \text{specific heat capacity of the body}$$
$$\Delta T: \text{Change in temperature of the body}$$
If $$Q\ \text{and}\ m$$ are constant,
$$\Delta T \propto \dfrac{1}{s}$$
So for small $$s, \Delta T$$ is more and hence it is better conductor of heat.
Which of the following behaves as insulator?
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Ebonite
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Mercury
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Silver
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Copper
Explanation
Ebonite is a very good insulator as it is a non-metal while mercury, silver and copper are examples of conductors because these three are metals.
Air is a _______ conductor of heat.
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Good
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Bad
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Both
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None
Explanation
All gases are poor conductor of heat. So air being a mixture of gases is also a poor conductor of heat.
Define good conductors of heat.
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Substances that can easily melt are called good conductors of heat.
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Substances through which heat can pass easily are called good conductors of heat.
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Substances through which heat cannot pass easily are called good conductors of heat.
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Substances that cannot easily melt are called good conductors of heat.
Explanation
Good conductors of heat are substances through which heat can pass easily.
Conductors become hot easily because they have:
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high specific capacity
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low specific heat capacity
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high freezing point
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low freezing point
Explanation
In conduction, heat is transferred by the vibrations of molecules. The density of conductors is large, it means molecules are close to each other. Because of that they can easily transfer the heat quickly throughout the whole volume of the conductor. Thus, less heat is needed to raise the temperature of unit mass of the conductors by $$1^oC$$. This heat is called specific heat capacity. Therefore conductors become hot easily on account of low specific heat capacity.
Conductors require __________ heat energy to get heated.
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More
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Same
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Less
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neutral
Explanation
Conductors have very low specific heat capacity (c), therefore heat required $$(Q)$$ to raise their temperature to a certain range is also less by the following relation:
$$Q\propto c$$
In general, metals have very low :
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Boiling Point
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Freezing Point
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Melting Point
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Resistivity
Explanation
In general, metals are good conductors. So they offer less resistance to the flow of current. Thus, metals have very low resistivity.
By the process of convection, the transfer of heat is always
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Vertically downwards
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Vertically upwards
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Both
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None
Explanation
By the process of convection, heat is always transferred vertically upwards. This happens because the medium particles near the source of heat absorb heat from the source, their volume expands, their density becomes lighter and they start moving upwards.
_________ is a process of transfer of heat by the actual movement of the medium particles.
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Conduction
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Convection
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Radiation
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All
Explanation
Convection is a process of transfer of heat by the actual movement of the medium particles. A medium is required for the transfer of heat by convection.
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