Q1. What is the correct formula for the rate of heat transfer (q) through a plane wall of thickness l and surface are A, when temperature difference between two surfaces is ΔT ? The thermal conductivity is k.

a. q = (k A ΔT) / l
b. q = k A l ΔT
c. q = (ΔT) / (k A l)
d. none of the above

ANSWER: a. q = (k A ΔT) / l

Q2. Thermal conductivity of the same material varies with

a. the thickness of the material
b. the temperature of the material
c. both a. and b.
d. thermal conductivity of the same martial does not vary at all

ANSWER: b. the temperature of the material

Q3. The surface temperatures of a plate with thickness of 0.06 m are 100°C and 40°C. The thermal conductivity (k) of wall is 350 W/mK. What is the rate of heat transfer through the plate in kW/m2?

a. 350000
b. 350
c. 35
d. 0.35

Q4. How does the thermal conductivity of a material change with respect to change in temperature of the same material?

a. thermal conductivity of a material increases with increase in its temperature
b. thermal conductivity of a material decreases with increase in its temperature
c. thermal conductivity of a material remains same with change in its temperature
d. unpredictable