Thermal Conductivity: Definition, Factors, and Applications in Materials Science

Question 1

Which of the following materials has the highest thermal conductivity?

Accepted Answer

Copper

Answer

Wood

Answer

Air

Answer

Steel

Question 2

A material with high thermal conductivity will:

Accepted Answer

Transfer heat rapidly

Answer

Resist heat transfer

Answer

Expand significantly with heat

Answer

Melt at a lower temperature

Question 3

Which of these factors DOES NOT directly influence the thermal conductivity of a material?

Accepted Answer

Color

Answer

Crystal Structure

Answer

Density

Answer

Temperature

Question 4

In a heat exchanger, a material with high thermal conductivity is primarily used to:

Accepted Answer

Facilitate rapid heat transfer between fluids

Answer

Prevent heat loss to the surroundings

Answer

Act as an insulator against heat transfer

Answer

Absorb and store heat

Question 5

Which method is NOT typically used to measure thermal conductivity?

Accepted Answer

Spectrophotometry

Answer

Laser Flash Method

Answer

Steady-State Method

Answer

Hot Wire Method

Question 6

A material with low thermal conductivity is commonly used as an:

Accepted Answer

Insulator

Answer

Heat sink

Answer

Thermoelectric material

Answer

Conductor

Question 7

Why is thermal conductivity a crucial consideration when designing engine components?

Accepted Answer

To manage heat dissipation and prevent overheating

Answer

To enhance the strength of the components

Answer

To improve fuel efficiency of the engine

Answer

To reduce the weight of the engine

Question 8

Which statement is TRUE regarding the effect of temperature on thermal conductivity?

Accepted Answer

For most materials, thermal conductivity generally increases with increasing temperature.

Answer

Thermal conductivity is independent of temperature.

Answer

Thermal conductivity always decreases with increasing temperature.

Question 9

A material with high thermal conductivity is preferred in applications where:

Accepted Answer

Rapid heat transfer is desired

Answer

Heat insulation is required

Answer

Heat reflection is important

Answer

Heat storage is essential

Question 10

A material with a thermal conductivity of 0.25 W/m·K is placed between two surfaces maintained at temperatures of 100°C and 20°C. What is the heat flux through the material?

Accepted Answer

(a) 200 W/m²

Answer

(c) 300 W/m²

Answer

(d) 350 W/m²

Answer

(b) 250 W/m²

Question 11

Thermal conductivity (k) of a material is defined as the amount of heat (Q) transferred per unit time (t) through a unit area (A) under a unit temperature gradient (dT/dx). Which equation correctly represents this definition?

Accepted Answer

k = Q/(t*A*(dT/dx))

Answer

k = Q*A*t/(dT/dx)

Answer

k = (dT/dx)/(Q*A*t)

Answer

k = t*A*(dT/dx)/Q

Question 12

Which of the following factors does NOT directly influence the thermal conductivity of a material?

Accepted Answer

(a) Pressure

Answer

(c) Composition

Answer

(d) Temperature

Answer

(b) Density

Question 13

A composite wall consists of three layers of different materials with thermal conductivities k1, k2, and k3, and thicknesses L1, L2, and L3, respectively. What is the overall thermal conductivity (k) of the composite wall?

Accepted Answer

(a) k = (L1/k1 + L2/k2 + L3/k3)^-1

Answer

(d) k = L1*k1 + L2*k2 + L3*k3

Answer

(c) k = (k1*L1 + k2*L2 + k3*L3)/(L1 + L2 + L3)

Answer

(b) k = (k1/L1 + k2/L2 + k3/L3)

Question 14

In a heat exchanger, the rate of heat transfer (Q) is directly proportional to the temperature difference (dT) between the hot and cold fluids and the heat transfer area (A). The proportionality constant is known as:

Accepted Answer

(a) Overall heat transfer coefficient (U)

Answer

(c) Thermal conductivity

Answer

(d) Specific heat capacity

Answer

(b) Nusselt number

Question 15

Which of the following materials generally has the highest thermal conductivity?

Accepted Answer

(a) Copper

Answer

(c) Air

Answer

(b) Rubber

Answer

(d) Wood

Question 16

A cylindrical rod of length L and diameter D is made of a material with thermal conductivity k. The rod is subjected to a temperature difference dT between its ends. What is the rate of heat transfer (Q) through the rod?

Accepted Answer

(a) Q = (pi*D^2*k*dT)/(4*L)

Answer

(d) Q = (pi*D^2*L*dT)/(4*k)

Answer

(b) Q = (4*L*k*dT)/(pi*D^2)

Answer

(c) Q = (L*D^2*k*dT)/(4*pi)

Question 17

The thermal conductivity of a material can be experimentally determined using a:

Accepted Answer

(a) Guarded hot plate apparatus

Answer

(b) Thermocouple

Answer

(c) Anemometer

Answer

(d) Calorimeter

Question 18

In a thermal insulation application, a material with which of the following properties is generally desirable?

Accepted Answer

(a) Low thermal conductivity

Answer

(d) High thermal conductivity

Answer

(c) High specific heat capacity

Answer

(b) Low density

Question 19

The thermal conductivity of a fluid:

Accepted Answer

(a) Can vary with temperature and pressure.

Answer

(c) Is independent of density.

Answer

(d) Is always constant.

Answer

(b) Is inversely proportional to viscosity.

Question 20

Which of the following heat transfer mechanisms is primarily governed by thermal conductivity?

Accepted Answer

Conduction

Answer

Convection

Answer

Evaporation

Answer

Radiation