Heat - Class 7 - Science
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Extra Questions - Heat | Lakhmir Singh | Science | Class 7
The percentage of carbon dioxide in exhaled air is $\qquad$
A) $21%$
B) $0.04%$
C) $4.4%$
D) $16.4%$
The correct answer is Option C: $4.4%$.
Exhalation is the process during which air is expelled from the lungs. This occurs when the diaphragm relaxes and moves upward, compressing the lungs and forcing the air out. The percentage of carbon dioxide in exhaled air is approximately $4.4%$.
Calculate standard free energy change for the reaction $\frac{1}{2} \mathrm{Cu}(\mathrm{s}) + \frac{1}{2} \mathrm{Cl}_{2}(\mathrm{~g}) \rightleftharpoons \frac{1}{2} \mathrm{Cu}^{2+} + \mathrm{Cl}^{-}$ taking place in a cell whose standard e.m.f. is 1.02 volts.
A) $-98430 \mathrm{~J}$
B) $98430 \mathrm{~J}$
C) $96500 \mathrm{~J}$
D) $-49215 \mathrm{~J}$
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Sign up nowVery Short Answer - Heat | Lakhmir Singh | Science | Class 7
State the unit in which temperature is commonly measured.
The unit in which temperature is commonly measured is degree Celsius (denoted as ${ }^{\circ} \mathrm{C}$).
What is the normal temperature of human body on Celsius scale?
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Sign up nowWhat is the name of those thermometers which do not use mercury?
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Sign up nowState whether water is a good convector of heat or a good conductor of heat.
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Sign up nowHow does the heat from the sun reach the earth?
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Sign up nowShort Answers - Heat | Lakhmir Singh | Science | Class 7
Why is a frying pan made of metal (like aluminium or stainless steel) but the handle of frying pan is made of plastic (or wood)?
A frying pan is made of metals like aluminium or stainless steel because these materials are good conductors of heat. This allows the pan to quickly transfer the heat from the stove to the food. However, the handle is made of plastic or wood because these materials are poor conductors of heat (or insulators of heat), which prevents the handle from becoming hot and makes it safe to hold.
Why are cooking utensils provided with handles made of plastic (or wood)?
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Sign up nowExplain why, it is difficult to hold a stainless steel tumbler containing very hot tea in the hand but a thermocol cup containing the same hot tea can be held easily.
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Sign up nowLong Answers - Heat | Lakhmir Singh | Science | Class 7
Explain how woollen clothes keep us warm during cold winter days. Discuss why wearing more layers of clothing during winter keeps us warmer than wearing just one thick piece of clothing.
Woollen clothes keep us warm during cold winter days because wool is a poor conductor of heat, which means it does not allow body heat to escape easily. Additionally, wool traps air within its fibres, and air is a very good insulator of heat. This trapped air stops the flow of heat from our warm bodies to the cold surroundings. Wearing multiple layers of clothing during winter is more effective than wearing one thick piece because additional layers trap more air, creating more insulation. This extra trapped air acts as a barrier that prevents body heat from escaping, keeping us warmer.
What is a clinical thermometer ? What is the range of a clinical thermometer ? Explain why, a clinical thermometer cannot be used to measure high temperatures.
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Sign up nowDefine radiation. Give any two examples where heat is transferred by radiation. What is the name of invisible heat rays which transfer heat by radiation?
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Sign up nowMCQ - Heat | Lakhmir Singh | Science | Class 7
A wooden spoon is dipped in a cup of ice cream. Its other end :
(a) becomes cold by the process of conduction.
(b) becomes cold by the process of convection.
(c) becomes cold by the process of radiation.
(d) does not become cold.
The process by which heat is transferred from the cold ice cream to the other end of the wooden spoon is called conduction. Conduction is the transfer of heat through a material without the material itself moving. This is possible because heat moves along the spoon from the warmer end (near the ice cream) to the cooler end (the end not in the ice cream) through the vibration and movement of the molecules in the spoon.
Given the options, the correct answer is:
(a) becomes cold by the process of conduction.
The device used for measuring temperature is called:
(a) tachometer
(b) odometer
(c) thermometer
(d) barometer
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Sign up nowThe woollen clothes keep us warm during winter because :
A. Wool is an insulator
B. Wool is a conductor
C. Wool traps air
D. Wool has vacuum
(a) A and B
(b) B and C
(c) C and D
(d) A and C
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Sign up nowThe process which can transfer heat through the vacuum as well as air is :
(a) conduction
(b) convection
(c) irradiation
(d) radiation
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Sign up nowHOTS - Heat | Lakhmir Singh | Science | Class 7
The bulb of thermometer A is coated with lampblack and the bulb of thermometer B is coated with silver. Both the thermometers are placed in sunshine for equal time :
(a) Which thermometer will show a higher rise in temperature?
(b) What conclusion is obtained from the above observation?
(a) Thermometer A will show a higher rise in temperature.
(b) The observation leads to the conclusion that objects with dark surfaces (like lampblack) absorb heat radiations more effectively than objects with light or reflective surfaces (like silver). Thus, dark-colored surfaces are better absorbers of heat compared to light-colored, reflective surfaces.
One end of the objects such as a steel spoon, a plastic scale, a pencil and a divider is put in a beaker of hot water. In which of these objects the other end will get hot? Why?
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