# Engineering Physics Questions and Answers – Thermal Conductivity

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

1. When one end of the rod is heated, the molecules at the hot end vibrate with higher amplitude and transmit the heat from one particle to the adjacent particle and so on. What is the process?
a) Convection
b) Conduction
d) Transmittance

Explanation: In the above condition, heat is transmitted by the vibration of particles. Conduction is the process in which heat is transferred from hotter end to colder end without the actual motion of particles. Therefore, it is conduction.

2. Solids with weekly bonded electrons are good conductors of heat.
a) True
b) False

Explanation: Transmission of heat depends upon the outermost electrons. Therefore solids with weekly bonded electrons are good conductors of heat.

3. When potassium is added to water, it is seen that the lower region becomes warm first and becomes less dense. It then moves up and the more dense cold water comes down and the process goes on. What is the process taking place?
b) Conduction
c) Convection
d) Purification

Explanation: Convection is the process in which heat is transmitted from hotter end to colder end by actual movement of heated particles. Since the particles are actually moving in the above process, it is convention.

4. Why is the roof of buildings painted white?
c) Because it is cheaper
d) Because it conducts heat

Explanation: Black objects are good absorbers and radiators while white surfaces are poor absorbers and radiators. Therefore houses are painted white to keep the building cool during summer.

5. What happens when a material is heated?
a) It contracts
b) It melts
c) It expands
d) It bursts

Explanation: Most materials expand on heating because the particles are moving about a higher average speed and therefore have a higher energetic collision.

6. Why locations next to large water bodies tend to have a moderate climate than those further inland?
a) Because of the latitude
b) Because of specific heat of water
c) Because of the heating effects of sun
d) Because of the water in clouds

Explanation: It takes a longer time to heat up or cool down a given mass of water than an equal mass of aluminium or iron. This high specific heat of water makes it easy for cooling and warming. This is why the locations next to larger water bodies tend to have a moderate climate than those further inland.

7. The outer ends of two bars A and B are at 100°C and 50° respectively. Calculate the temperature at the welded joint if they have the same cross-section and the same length and their thermal conductivities are in the ratio of A:B = 7:5.
a) 79.166°C
b) 80.548°C
c) 20.157°C
d) 58.147°C

Explanation: K1/K2 = (θ2-θ3)/(θ1-θ2)
θ2= 79.166℃

8. What happens when you heat china having some dark paintings engraved on it at 1000°C and then examine it in a dark room immediately?
a) The dark painting will appear much brighter
b) The whole china dish will be bright
c) The china dish doesn’t glow
d) The china dish will develop patterns

Explanation: According to Kirchhoff’s law, if a body strongly absorbs radiation of a certain wavelength, it must emit strongly the radiation of the same wavelength. The dark paintings are better absorbers, and therefore, also better emitters.

9. A green glass heated in a furnace when taken out in dark glows red.
a) False
b) True

Explanation: Green glass, when cold, is a good absorber of red light and a good reflector of green light. When heated, it becomes a good emitter of red light in accordance with Kirchhoff’s law.

10. Two thermometers are constructed in the same way except that one has a spherical bulb and the other an elongated cylindrical bulb. Which of the two will respond quickly to temperature changes?
a) Spherical bulb
b) Elongated cylindrical bulb
c) All of the mentioned
d) None of the mentioned

Explanation: A cylindrical bulb has a greater surface area than a spherical bulb of the same volume. Hence the thermometer with elongated cylindrical bulb will respond to temperature changes more quickly than the one with a spherical bulb.

11. The temperature of a body can be negative on the Kelvin scale.
a) True
b) False

Explanation: The temperature of a body cannot be negative on a Kelvin scale because the absolute zero on the Kelvin scale is the minimum possible temperature.

12. Which of the following is an effective coolant?
a) Oil
b) Mercury
c) Water
d) Acids

Explanation: The specific heat of water is very high. When it runs over hot parts of the engine or machinery, it absorbs a large amount of heat. This helps in maintaining the temperature of the engine low.

Sanfoundry Global Education & Learning Series – Engineering Physics.

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