Questions

[1 Mark Question Answer]

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16 questions · timed · auto-graded

Question 11 Mark
Explain the following :
Why are sintex water tank painted white in hot countries?
Answer
The water stored in the white sintex tank keeps cold because of less absorption and a good reflection of radiant heat from the white body.
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Question 21 Mark
Explain the following :
Why do we wear dark coloured or black clothes during winter?
Answer
The transfer of heat by radiation process does not require any medium. We prefer wearing dark-coloured clothes in winter because dark surfaces absorb more heat than light surfaces.
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Question 31 Mark
Explain the following :
Why do we wear white or light coloured clothes in summer?
Answer
We prefer white coloured clothes in summer because white colour is poor absorber of heat and so they keep us cool during summer.
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Question 41 Mark
Explain the following :Why does a marble floor feel colder in winter than a carpeted floor?
Answer
The marble floor which transmits heat energy easily feels colder and the carpet floor which does not allow heat to transmit feels warmer.
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Question 51 Mark
Explain the following :Why are ice blocks wrapped in saw dust of woolen blanket?
Answer
The sawdust or woolen blanket contains a large amount of trapped air, which acts as an insulator and does not allow the heat from outside to reach the ice.
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Question 61 Mark
Explain the following :Why are the cooking pots provided with plastic or wooden handles?
Answer
Wood and plastic are bad conductors of heat. So, we can hold the pots with wooden or plastic handles directly, without burning our hands.
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Question 71 Mark
Explain the following :Why are the houses with thatched roofs cooler in summer than the concrete houses?
Answer
Thatched roof contains a large amount of trapped air. The heat from outside does not flow inside through the roofs because air is a bad conductor of heat. Thus the houses remain cool in summer.
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Question 81 Mark
Explain the following :Why do the birds puff up their feathers on a cold day?
Answer
Birds puff up their feathers in winter because by doing so they trap a large amount of air in their body which in turn acts as an insulator and does not allow the heat from their bodies to flow out.
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Question 91 Mark
Explain the following :Why do we wear loose woolen clothes in winter?
Answer
We wear woolen clothes because they trap the bodies heat to keep us warm. On the other hand, thick and dark-coloured clothing is good in winter as it absorbs the sun’s rays to keeps us warm.
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Question 101 Mark
What are bad conductors? Give four examples of bad conductors.
Answer
The materials which do not allow heat to pass through them easily are known as bad conductors. Examples: Glass, mica, ebonite, cotton, wool, etc.
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Question 111 Mark
What are good conductors? Give four examples of good conductors.
Answer
The materials which allow heat to transfer through it easily are known as good conductors of heat. Examples: Silver, iron, copper, aluminum, etc.
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Question 121 Mark
Given below statement is incorrect. Write the correct statement :
A wooden chair feels colder than an iron chair in winter.
Answer
A wooden chair feels not colder than an iron chair in winter.
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Question 131 Mark
Given below statement is incorrect. Write the correct statement :
The inner and outer surface of a vacuum flask are painted white.
Answer
The inner and outer surface of a vacuum flask are silvered.
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Question 141 Mark
Given below statement is incorrect. Write the correct statement :
Shining bodies are good absorbers and good radiators of heat energy.
Answer
Shining bodies are poor absorbers and poor radiators of heat energy.
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Question 151 Mark
Given below statement is incorrect. Write the correct statement :
Heat from the sun reaches the earth by the process of convection.
Answer
Heat from the sun reaches the earth by the process of radiation.
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Question 161 Mark
Given below statement is incorrect. Write the correct statement :
Convection currents are possible in solids.
Answer
Convection currents are not possible in solids.
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[1 Mark Question Answer] - PHYSICS STD 7 Questions - Vidyadip