Engineering Physics Multiple Choice Questions 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
c) Radiation
d) Transmittance
Answer: b
Clarification: 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
Answer: a
Clarification: 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?
a) Radiation
b) Conduction
c) Convection
d) Purification
Answer: c
Clarification: 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?
a) Because it absorbs radiation
b) Because it reflects radiations
c) Because it is cheaper
d) Because it conducts heat
Answer: b
Clarification: 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
Answer: c
Clarification: 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
Answer: b
Clarification: 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
Answer: a
Clarification: 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