1. Mark the matter with least value of thermal conductivity
a) Air
b) Water
c) Ash
d) Window glass
Explanation:For air, it is .024 W/ m degree i.e. lowest.
2. Which one of the following forms of water have the highest value of thermal conductivity?
a) Boiling water
b) Steam
c) Solid ice
d) Melting ice
Explanation: For ice, it is 2.25 W/m degree i.e. maximum.
3. Low temperature insulation are used when the enclosure is at a temperature lower than the ambient
temperature. Which one of the following is not a low temperature insulation?
a) Asbestos
b) Cork
c) Cattle hair
d) Slag wool
Explanation: Asbestos is a high temperature insulation which is used when it is desired to prevent an enclosure at a temperature higher than the ambient from losing heat to its surroundings.
4. The average thermal conductivities of water and air conform to the ratio
a) 50:1
b) 25:1
c) 5:1
d) 15:1
Explanation: For water, it is 0.55-0.7 W/m degree and for air it is .024 W/m degree.
5. Identify the very good insulator
a) Saw dust
b) Cork
c) Asbestos sheet
d) Glass wool
Explanation: Glass wool has a lowest thermal conductivity of 0.03 W/m degree amongst given option
6. 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. Heat conduction in gases is due to
a) Elastic impact of molecules
b) Movement of electrons
c) EM Waves
d) Mixing of gases
Explanation: If there is elastic collision then after sometime molecules regain its natural position.
8. The heat energy propagation due to conduction heat transfer will be minimum for
a) Lead
b) Water
c) Air
d) Copper
Explanation: It is because air has lowest value of thermal conductivity amongst given options.
9. 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. Choose the false statemen
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