# Engineering Physics Questions and Answers – Temperature and Specific Heat

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

1. A quantity of heat required to change the unit mass of a solid substance, from solid state to liquid state, while the temperature remains constant, is known as ___________
a) Latent heat
b) Sublimation
c) Hoar frost
d) Latent heat of fusion

Explanation: The amount of heat required to change the state of the unit mass of a substance from solid at its melting point is called latent heat of fusion.

2. A constant pressure air thermometer gave a reading of 47.5 units of volume, when immersed in ice-cold water, and 67 units in a boiling liquid. What is the boiling point of the liquid?
a) 100°C
b) 112°C
c) 125°C
d) 135°C

Explanation: From Charles’s law,
V1/T1 = V2/T2
47.5/(0+273)=67/T2
T2=(67×273)/47.5=385K
T2=112°C.

3. The bulb of one thermometer is spherical, while that of other is cylindrical. If both of them have an equal amount of mercury, which one will respond quickly to the temperature?
a) Spherical
b) Cylindrical
c) Elliptical
d) Circle

Explanation: As the square area of a cylindrical bulb is larger than a spherical bulb, heat will be transmitted quickly through a cylindrical bulb and it will respond quickly to the temperature.
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4. A black body at a high temperature T K radiates energy at the rate of E Wm-2. When the temperature falls to T/2 K, the radiated energy will be ___________
a) E/4
b) E/2
c) 2E
d) E/16

Explanation: E/E=((T/2)/T)4=1/16
E=E/16.

5. On increasing the temperature of a substance gradually, its colour becomes ___________
a) Red
b) Green
c) Yellow
d) White

Explanation: By Wien’s law
ʎm is proportioanl to 1/T
On increasing temperature, wavelength decreases. As yellow colour has minimum wavelength, the substance gradually becomes yellow.

6. Assertion: Good conductors of heat are also good conductors of electricity and vice-versa.
Reasons: Mainly electrons are responsible for these conductors.
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: Both the assertion and reason are true. Good conductors have a large number of free electrons which make them good conductors both heat and electricity.

7. A centigrade and Fahrenheit thermometers are dipped in boiling water. The water temperature is lowered until the Fahrenheit thermometer registers 140°. What is the fall in temperature registered by the centigrade thermometer?
a) 80°C
b) 60°C
c) 360°C
d) 30°C

Explanation: C/5=(F-32)/9=(140-32)/9=108/2=12
C=60°C
On centigrade scale, the boiling point of water is 100. Therefore, fall in temperature registered by the centigrade thermometer = 100-60 = 40°C.

8. If 1g of steam is mixed with 1g of ice, what is the resultant temperature of the mixture?
a) 270°
b) 230°
c) 100°
d) 50°

Explanation: Heat required to change 1g of ice at 0°C first into the water at 0°C and then into the water at 100°C,
Q=mL+mc∆T=1×80+1×1×100=180cal
Now 1g of steam carries 540cal of heat when 1g of steam is mixed with 1g of ice, entire steam will not condense. Finally, we will have a mixture of water and steam at 100°C.

9. A beaker full of hot water is kept in a room. If it cools from 80°C to 75°C in t1 minutes, from 75°C to 70°C in t2 minutes and from 70°C to 65°C in t3 minutes, then ___________
a) t1=t2=t3
b) t1 < t2 = t3
c) t1 < t2 < t3
d) t1 > t2 > t3

Explanation: According to Newton’s law of cooling, Rate of cooling is proportional to temperature difference of the body and its surroundings.
As the temperature of the body approaches the room temperature, rate of cooling decreases.
t1 < t2 < t3.

10. A black body is at 727°C. It emits energy at a rate, which is proportional to ___________
a) (727)2
b) (1000)2
c) (727)4
d) (1000)4

Explanation: Eα(273+727)4
Eα(1000)4.

11. Gas thermometers are more sensitive than a mercury thermometer.
a) True
b) False

Explanation: The coefficient of expansion of a gas in very large as compared to the coefficient of expansion of mercury. For the same temperature range, a gas would undergo a much larger change in volume as compared to mercury.

12. A spherical body of area A and emissivity e = 0.6 is kept inside a perfectly black body. Energy radiated per second by the body at temperature T is ___________
a) 0.4σAT4
b) 0.8 σAT4
c) 0.6 σAT4
d) 1.0 σAT4

Explanation: According to Stefan’s law, energy radiated per second by a body of emissivity e at a temperature T,
E = e σAT4
E = 0.6 σAT4.

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