Heat and Mass Transfer MCQs

Question 1

Thermal diffusivity of a substance is

Accepted Answer

All of the above

Answer

Directly proportional to the thermal conductivity

Answer

Inversely proportional to density of substance

Answer

Inversely proportional to specific heat

Question 2

The insulation ability of an insulator with the presence of moisture would

Accepted Answer

Decrease

Answer

Increase

Answer

Remain unaffected

Answer

May increase/decrease depending on temperature and thickness of insulation

Question 3

The transfer of heat by molecular collision is smallest in

Accepted Answer

Gases

Answer

Solids

Answer

Liquids

Answer

None of these

Question 4

According to Stefan Boltzmann law, the total radiation from a black body per second per unit area is directly proportional to the

Accepted Answer

Fourth power of the absolute temperature

Answer

Absolute temperature

Answer

Square of the absolute temperature

Answer

Cube of the absolute temperature

Question 5

Cork is a good insulator because it has

Accepted Answer

Porous body

Answer

Free electrons

Answer

Atoms colliding frequency

Answer

Low density

Question 6

Pick up the wrong case. Heat flowing from one side to other depends directly on

Accepted Answer

Thickness

Answer

Face area

Answer

Time

Answer

Temperature difference

Question 7

Thermal conductivity of solid metals with rise in temperature normally

Accepted Answer

Decreases

Answer

Increases

Answer

Remain constant

Answer

May increase or decrease depending on temperature

Question 8

The heat transfer by conduction through a thick sphere is given by

Accepted Answer

$${	ext{Q}} = \frac{{4\pi {	ext{k}}{{	ext{r}}_1}{{	ext{r}}_2}\left( {{{	ext{T}}_1} - {{	ext{T}}_2}} ight)}}{{{{	ext{r}}_2} - {{	ext{r}}_1}}}$$

Answer

$${	ext{Q}} = \frac{{2\pi {	ext{k}}{{	ext{r}}_1}{{	ext{r}}_2}\left( {{{	ext{T}}_1} - {{	ext{T}}_2}} ight)}}{{{{	ext{r}}_2} - {{	ext{r}}_1}}}$$

Answer

$${	ext{Q}} = \frac{{6\pi {	ext{k}}{{	ext{r}}_1}{{	ext{r}}_2}\left( {{{	ext{T}}_1} - {{	ext{T}}_2}} ight)}}{{{{	ext{r}}_2} - {{	ext{r}}_1}}}$$

Answer

$${	ext{Q}} = \frac{{8\pi {	ext{k}}{{	ext{r}}_1}{{	ext{r}}_2}\left( {{{	ext{T}}_1} - {{	ext{T}}_2}} ight)}}{{{{	ext{r}}_2} - {{	ext{r}}_1}}}$$

Question 9

The value of the wave length for maximum emissive power is given by

Accepted Answer

Wine’s law

Answer

Kirchhoff’s law

Answer

Stefan’s law

Answer

Planck’s law