Engineering Physics Questions and Answers – Latent Heat

This set of Engineering Physics Multiple Choice Questions & Answers (MCQs) focuses on “Latent Heat”.

1. Same material is used to make a sphere, a cube and a thin circular plate and having the same mass. They are initially heated to a temperature of 3000°C. Which of these will cool fast?
a) Sphere
b) Cube
c) Plate
d) All thee will cool at the same rate

Explanation: All three have the same mass and hence the same volume. Therefore the plate has a maximum surface area. So, the plate will cool fastest.

2. Heat was given to a body, which raises its temperature by 1°C is ___________
a) Water equivalent
c) Thermal capacity
d) Specific heat

Explanation: Heat required to raise the temperature of a body through 1°C is called thermal capacity.

3. According to Newton’s law of cooling, the rate at which a body cools is proportional to (∆θ)n, where ∆θ is the difference if the temperature of the body and the surroundings. What is n equal to?
a) Two
b) Three
c) Four
d) One

Explanation: According to Newton’s law of cooling,
Rate of cooling is proportional to the temperature difference between the body and its surroundings
Therefore, n = 1.

4. If boiling point of water is 95°F, what will be reading at Celsius scale?
a) 7°C
b) 65°C
c) 63°C
d) 35°C

Explanation: C = 5/9(F-32)
C = 5/9(95-32)
C = 35°C.

5. 50g of ice at 0°C is mixed with 50g of water at 80°C, what will be the final temperature of a mixture?
a) 0°C
b) 40°C
c) 60°C
d) 4°C

Explanation: Heat required to melt 50g ice = mL = 50×80=4000cal
Heat given out by water in cooling from 80°C to 0 = mc∆T=50×1×80=4000cal
Heat given by water is just sufficient to melt the whole ice. So the final temperature is 0°C.

6. Assertion: Water kept in an open vessel will quickly evaporate on the surface of the moon.
Reason: The temperature at the surface of the moon is much higher than the boiling point of water.
a) Both assertion and reason are true and the reason is the correct explanation of the assertion
b) Both assertion and reason are true but the reason is not the correct explanation of the assertion
c) Assertion is true but the reason is false
d) Both assertion and reason are false

Explanation: The assertion is true but the reason is false. Evaporation occurs at all temperatures. Due to low gravity on moon, the escape velocity is small.

7. Assertion: In a pressure cooker the water is about to be boiled. The cooker is then removed from the stove. Now on removing the lid of the pressure cooker, the water boils again.
Reason: The impurities in water bring down its boiling point.
a) Both assertion and reason are true and the reason is the correct explanation of the assertion
b) Both assertion and reason are true but the reason is not a correct explanation of the assertion
c) Assertion is true but the reason is false
d) Both assertion and reason are false

Explanation: The assertion is true but the reason is false. When the lid is removed, the pressure decreases. This decreases the boiling point of water and water begins to boil.

8. The Wien’s displacement law expresses a relation between ___________
a) Wavelength corresponding to maximum energy and absolute temperature
c) Temperature and emissive power
d) Colour of light and emissive power

Explanation: Wien’s displacement law gives a relation between wavelength corresponding to maximum energy emitted by a black body and its absolute temperature.

9. Two containers A and B are partly filled with water and closed. The volume of A is twice that of B and it contains half the amount of water in B. If both are at same temperature, the water vapour in the containers will have pressure in the ratio of ___________
a) 1:2
b) 1:1
c) 2:1
d) 4:1

Explanation: Vapour pressure does not depend on the amount of the substance. It depends on temperature only.

10. The thermal capacity of 40g of aluminium (specific heat = 0.2 cal°g-1 C-1) is ___________
a) 40cal°C-1
b) 160 cal°C-1
c) 200 cal°C-1
d) 8 cal°C-1

Explanation: Thermal capacity = mc
Thermal capacity = 40g×0.2cal g-1 C-1
= 80 cal°C-1.

11. 80g of water at 30°C is poured on a large block of ice which is at 0°C. The mass of ice that melts is ___________
a) 30g
b) 80g
c) 150g
d) 1600g

Explanation: Heat used in melting m gram of ice = Heat lost by 80g water
mL=80×1×30
m=(80×1×30)/80=30g.

12. A constant volume gas thermometer using helium records a pressure of 20.0kPa at the triple point of water and pressure of 14.3 kPa at the temperature of ‘dry ice’. What is the temperature of dry ice?
a) 19.530K
b) 1.9530K
c) 195.30K
d) 1953.0K

Explanation: Temperature of dry ice,
T=P/Ptr ×Ttr=(14.3×273.16)/20
Temperature = 195.30K.

Sanfoundry Global Education & Learning Series – Engineering Physics.

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