Heat Transfer MCQ’s– Thermal Conductivity of Materials
1 - Question
Thermal conductivity is defined as the heat flow per unit time
a) When the temperature gradient is unity
b) Across the wall with no temperature
c) Through a unit thickness of the wall
d) Across unit area where the temperature gradient is unity
Explanation: Thermal conductivity of a material is because of migration of free electrons and lattice vibrational waves.
2 - Question
Mark the matter with least value of thermal conductivity
d) Window glass
Explanation: For air, it is .024 W/ m degree i.e. lowest.
3 - Question
Which one of the following forms of water have the highest value of thermal conductivity?
a) Boiling water
c) Solid ice
d) Melting ice
Explanation: For ice, it is 2.25 W/m degree i.e. maximum.
4 - Question
The average thermal conductivities of water and air conform to the ratio
Explanation: For water, it is 0.55-0.7 W/m degree and for air it is .024 W/m degree.
5 - Question
Identify the very good insulator
a) Saw dust
c) Asbestos sheet
d) Glass wool
Explanation: Glass wool has a lowest thermal conductivity of 0.03 W/m degree amongst given option.
6 - Question
Most metals are good conductor of heat because of
a) Transport of energy
b) Free electrons and frequent collision of atoms
c) Lattice defects
d) Capacity to absorb energy
Explanation: For good conductors, there must be electrons that are free to move.
7 - Question
Heat conduction in gases is due to
a) Elastic impact of molecules
b) Movement of electrons
c) EM Waves
d) Mixing of gases
Answer: a Explanation: If there is elastic collision then after sometime molecules regain its natural position.
8 - Question
The heat energy propagation due to conduction heat transfer will be minimum for
Explanation: It is because air has lowest value of thermal conductivity amongst given options.
9 - Question
Cork is a good insulator because
a) It is flexible
b) It can be powdered
c) Low density
d) It is porous
Explanation: Cork has thermal conductivity in the range of 0.05-0.10 which is very low so it can be porous.
10 - Question
Choose the false statement
a) For pure metal thermal conductivity is more
b) Thermal conductivity decreases with increase in the density of the substance
c) Thermal conductivity of dry material is lower than that of damp material
d) Heat treatment causes variation in thermal conductivity
Explanation: Thermal conductivity increase with increase in the density of a substance.