Heat Class 7 MCQ. We covered all the Heat Class 7 MCQ in this post for free so that you can practice well for the exam.
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MCQ on Heat for Class 7th Students
The temperature of a piece of metal is raised from 27 °C to 52 °C. The rate at which the metal radiates energy increases nearly
(A) 1.36 times
(B) 2 times
(C) 2.72 times
(D) 4.08 times
Option a – 1.36 times
The quantity of heat per unit of time which crosses a unit area of a metal plate during conduction depends upon
(A) the density of the metal.
(B) the temperature gradient perpendicular to the area.
(C) the temperature to which the metal is heated.
(D) the area of the metal plate.
Option b – the temperature gradient perpendicular to the area.
A body cools at the rate of 0.6 °C/s when it is 40 °C above the surrounding. The rate of cooling, when it is at 20 °C above the same surrounding will be
(A) 0.2 °C/s
(B) 0.3 °C/s
(C) 0.6 °C/s
(D) 0.4 °C/s
Option b – 0.3 °C/s
A heat flux of 4000 J/s is to be passed through a copper rod of length 10 cm and an area of cross-section of 100 cm². The thermal conductivity of copper is 400 W/m °C. The two ends of this rod must be kept at a temperature difference of
(A) 1°C
(B) 10 °C
(C) 100 °C
(D) 1000 °C
Option c – 100 °C
A body cools from 50 °C to 49.9 °C in 20 s. How long will it take approximately to cool from 40 °C to 39.9 °C? Assume the temperature of the surroundings to be 30 °C and Newton’s law of cooling to be valid.
(A) 10 s
(B) 40 s
(C) 2.5 s
(D) 5 s
Option b – 40 s
The lengths of the two rods made up of the same metal and having the same area of the cross-section are 0.6 m and 0.8 m respectively. The temperature between the ends of the first rod are 100 °C and 70 °C and that for the other rod are 160 °C and 120 °C. For which rod will the rate of conduction be greater?
(A) First
(B) Second
(C) Same for both
(D) Either in the first or second
Option c – Same for both
If the coefficient of absorption and coefficient of reflection of a surface of a body are 0.4 and 0.6 respectively, then ( Heat Class 7 MCQ )
(A) emissive power will be 0.2.
(B) transmission power will be 0.2.
(C) the body will be totally transparent.
(D) the body will be totally opaque.
Option d – the body will be totally opaque.
Two identical rods of copper and iron are coated with wax uniformly. When one end of each is kept at the temperature of boiling water, the length up to which wax melts are 8.8 cm and 4.4 respectively. If the thermal conductivity of copper is 0.92, then the thermal conductivity of iron is
(A) 0.23
(B) 0.46
(C) 0.115
(D) 0.69
Option a – 0.23
A calorie is defined as the amount of heat required to raise the temperature of 1 g of water by 1 certain condition. Which of the following conditions is true?
(A) From 14.5 °C to 15.5 °C at 760 mm of Hg
(B) From 98.5 °C to 99.5 °C at 760 mm of Hg
(C) From 13.5 °C to 14.5 °C at 76 mm of Hg
(D) From 3.5 °C to 4.5 °C at 76 mm of Hg
Option a – From 14.5 °C to 15.5 °C at 760 mm of Hg
The coefficient of absorption of the surface of a body is 0.25. When 100 calories of heat are incident on the body, 40 calories are reflected from its surface. Then the coefficient of transmission of the body is
(A) 0.25
(B) 0.35
(C) 0.4
(D) 0.5
Option b – 0.35
What is the value of Cp for a certain gas, if the ratio of specific heats is 3/2? ( Heat Class 7 MCQ )
(A) R
(B) 2R
(C) 3R
(D) 5R
Option c – 3R
Air is a bad conductor of heat or it partly conducts heat, still, a vacuum is to be generated between the walls of the thermos flask because
(A) it is difficult to fill the air between the walls of a thermos flask.
(B) due to more pressure of air, the thermos can get cracked.
(C) by convection, heat can flow through the air.
(D) on filling the air, there is no advantage.
Option c – by convection, heat can flow through the air.
Which of the following statement is incorrect? The greenhouse effect is responsible for global warming. Due to global warming, ………
(A) ice caps near the poles are melting faster.
(B) coastal buildings are in danger of getting submerged.
(C) the duration of the day will be more than 24 hours.
(D) the duration of the day will be less than 24 hours.
Option d – the duration of the day will be less than 24 hours.
Given that ‘p’ joule of heat is incident on a body and out of it ‘q’ joule is reflected and transmitted by it. The absorption coefficient of the body is
(A) p/q
(B) q/p
(C) (q-p)/p
(D) (p-q)/p
Option d – (p-q)/p
Three liters of water in a container are heated with a coil of 1 kW at 27 °C. The lid of the container is open and energy dissipates at the rate of 160 J/s. How much time is required to raise the temperature from 27 °C to 77 °C? (Given: specific heat of water is 4.2 kJ/kg)
(A) 7 min
(B) 6 min 2 s
(C) 12 min 30 s
(D) 14 min
Option c – 12 min 30 s
Two liquids at temperatures 60 °C and 20 °C respectively have masses in the ratio 4 : 5 and their specific heats in the ratio 4 : 3. If the two liquids are mixed, the resultant temperature is
(A) 70 °C
(B) 50 °C
(C) 40 °C
(D) 35 °C
Option d – 35 °C
One end of a metal rod of length 1.0 m and area of cross-section 100 cm² is maintained at 100 °C. If the other end of the rod is maintained at 0 °C, the quantity of heat transmitted through the rod per minute is (Coefficient of thermal conductivity of the material of rod = 100 W/m K)
(A) 3 × 10³ J
(B) 6 × 10³ J
(C) 9 × 10³ J
(D) 12 × 10³ J
Option b – 6 × 10³ J
Half part of an ice block is covered with black cloth and the rest half is covered with white cloth and then it is kept in sunlight. After some time, clothes are removed to see the melted ice. Which of the following statements is correct?
(A) Ice covered with a white cloth will melt more
(B) Ice covered with a black cloth will melt more
(C) Equal ice will melt under both clothes
(D) It will depend on the temperature of the surroundings of the ice
Option b – Ice covered with a black cloth will melt more
If the temperature of any ideal black body is reduced by two times, then the wavelength of maximum emission will be
(A) four times.
(B) halved.
(C) doubled.
(D) one fourth.
Option c – doubled.
The two ends of a metal rod are maintained at temperatures of 100 °C and 120 °C. The rate of heat flow in the rod is found to be 4.0 J/s. If the ends are maintained at temperatures 200 °C and 220 °C, the rate of heat flow will be
(A) 2 J/s
(B) 16 J/s
(C) 8.0 J/s
(D) 4.0 J/s
Option d – 4.0 J/s
A piece of lead weighing 500 g gives out 1600 calories of heat when it is cooled from 90 °C to 10 °C. Find its specific heat.
(A) 0.004 cal/g °C
(B) 4.4 cal/g °C
(C) 0.04 cal/g °C
(D) 0.4 cal/g °C
Option c – 0.04 cal/g °C
A piece of iron is heated in a flame. It first becomes dull red then becomes reddish yellow and finally turns to white hot. The correct explanation for the above observation is possible by using
(A) Stefan’s law.
(B) Wien’s displacement law.
(C) Kirchhoff’s law.
(D) Newton’s law of cooling.
Option b – Wien’s displacement law.
A black body radiates heat at temperatures T₁’ and T₂’ (T₂> T₁). The frequency corresponding to maximum energy is
(A) more at T₁.
(B) more at T₂.
(C) equal for T₁ and T₂.
(D) independent of T₁ and T₂.
Option b – more at T₂.
2 kg water at 60 °C is mixed with 1 kg of water at 30 °C kept in a vessel of heat capacity 200 J/K. The specific heat of water is 4200 J/kg K. Final temperature is nearly
(A) 55 °C
(B) 50 °C
(C) 45 °C
(D) 35 °C
Option b – 50 °C
Assertion: The energy radiated per second per unit area of a black body becomes 16 times if its temperature is doubled. Reason: This is the consequence of Stefan’s law.
(A) The assertion is True, Reason is True; Reason is a correct explanation for Assertion.
(B) The assertion is True, and Reason is True; Reason is not a correct explanation for Assertion.
(C) The assertion is True, Reason is False.
(D) The assertion is False, Reason is True.
Option a – The assertion is True, Reason is True; Reason is a correct explanation for Assertion.
Assertion: If the thermal conductivity of a solid is 4, then its thermal resistivity is 0.25. Reason: Thermal resistivity is the reciprocal of thermal conductivity.
(A) Assertion is True. The reason is True: Reason is a correct explanation for Assertion.
(B) The assertion is True, and Reason is True: Reason is not a correct explanation for Assertion.
(C) The assertion is True, Reason is False.
(D) The assertion is False, Reason is True.
Option a – Assertion is True. The reason is True: Reason is a correct explanation for Assertion.
200 g of water at 50 °C was added to 100 g of ice at 0 °C. The final temperature of the mixture at equilibrium will be around
(A) 3.33 °C
(B) 6.66 °C
(C) 9.99 °C
(D) 16.66 °C
Option b – 6.66 °C
Three bodies of the same material and having masses m, 2m, and 3m are at temperatures 40 °C, 50 °C, and 60 °C respectively. If the bodies are brought in thermal contact, the final temperature will be
(A) 58 °C
(B) 53 °C
(C) 35 °C
(D) 48 °C
Option b – 53 °C
When 2.5 kg of ice melts at 0 °C, its volume decreases by 10%. The latent heat of ice is 80 kcal/kg. Internal latent heat L, of ice, is
(A) 80 kcal/kg
(B) greater than 80 kcal/kg
(C) smaller than 80 kcal/kg
(D) zero
Option b – greater than 80 kcal/kg
A body cools at the rate of 3 °C/min when its temperature is 50 °C. If the temperature of its surroundings is 25 °C, then the rate of cooling of the body at 40 °C will be
(A) 2 °C/min
(B) 1.5 °C/min
(C) 1.2 °C/min
(D) 1.8 °C/min
Option d – 1.8 °C/min
The ends of two rods of different materials with their thermal conductivities, radii of cross-sections, and lengths are in the ratio 1 : 2 and are maintained at the same temperature difference. If the rate of flow of heat in the larger rod is 8 cal/s, that in the shorter rod in cal/s will be
(A) 2
(B) 1
(C) 8
(D) 16
Option a – 2
A body cools from 100 °C to 70 °C in 8 minutes. If the room temperature is 15 °C, the time taken to cool from 70 °C to 40 °C will be
(A) 14 minutes
(B) 7 minutes
(C) 8 minutes
(D) 16 minutes
Option a – 14 minutes
1 gram of ice is mixed with 1 gram of steam. At thermal equilibrium, the temperature of the mixture is
(A) 50 °C
(B) 0°C
(C) 55 °C
(D) 100 °C
Option d – 100 °C
The temperature of a black body increases from 327 °C to 927 °C and the initial energy possessed is 2 kJ. What is its final energy?
(A) 32 kJ
(B) 320 kJ
(C) 1200 kJ
(D) 120 kJ
Option a – 32 kJ
For cooking the food, which of the following types of utensils is most suitable? ( Heat Class 7 MCQ )
(A) High specific heat and low conductivity.
(B) High specific heat and high conductivity.
(C) Low specific heat and low conductivity.
(D) Low specific heat and high conductivity.
Option d – Low specific heat and high conductivity.
What is required for heat to flow from one part of a solid to another part? ( Heat Class 7 MCQ )
(A) Uniform density.
(B) Density gradient.
(C) Temperature gradient.
(D) Uniform temperature.
Option c – Temperature gradient.
Mud houses are cooler in summer and warmer in winter because ( Heat Class 7 MCQ )
(A) mud is a superconductor of heat.
(B) mud is a good conductor of heat.
(C) mud is a bad conductor of heat.
(D) mud reflects heat.
Option c – mud is a bad conductor of heat.
The heat flows through a rod of length 50 cm and an area of cross-section of 5 cm². Its ends are 25 °C and 125 °C respectively. The coefficient of thermal conductivity of the material of the rod is 0.092 kcal/ms °C. The temperature gradient in the rod is
(A) 2 °C/cm
(B) 2 °C/m
(C) 20 °C/cm
(D) 20 °C/m
Option a – 2 °C/cm
A metal sphere cools from 64 °C to 55 °C in 10 minutes and to 42 °C in the next 10 minutes. The ratio of the rate of fall of temperature in the two intervals is
(A) 9/10
(B) 13/10
(C) 9/13
(D) 13/9
Option c – 9/13
Which of the following cylindrical rods will conduct the most heat, when their ends are maintained at the same steady temperature?
(A) Length 1 m; radius 1 cm
(B) Length 2 m; radius 1 cm
(C) Length 2 m; radius 2 cm
(D) Length 2 m; radius 4 cm
Option d – Length 2 m; radius 4 cm
We covered all the heat class 7 MCQ above in this post for free so that you can practice well for the exam.
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