### Heat Transfer

11. ccording to Kirchoff's law, the ratio of emissive power to absorptivity for all bodies is equal to the emissive power of a

1. grey body
2. brilliant white polished body
3. red hot body
4. black body
5. none of the above.

black body

12. ccording to Stefan-Boltzmann law, ideal radiators emit radiant energy at a rate proportional to

1. absolute temperature
2. square of temperature
3. fourth power of absolute temperature
4. fourth power of temperature
5. cube of absolute temperature.

fourth power of absolute temperature

13. ccording to Stefan's law, the total radiation from a black body per second per unit area is proportional to

1. absolute temperature
2. T2
3. T5
4. t
5. l/T.

t

14. ccording to Wien's law, the wavelength corresponding to maximum energy is proportion to

1. absolute temperature (T)
2. I2
3. f
4. t
5. 1/r.

absolute temperature (T)

15. Cork is a good insulator because it has

1. free electrons
2. atoms colliding frequency
3. low density
4. porous body
5. all of the above.

porous body

16. Depending on the radiating properties, body will be transparent when

1. p = 0, x = 0 and a = 1
2. p=l,x = 0,anda = 0
3. p = 0, T= l,anda = 0
4. X = 0, a + p = 1
5. a = 0,x + p= 1.

p = 0, T= l,anda = 0

17. Emissivity of a white polished body in comparison to a black body is

1. higher
2. lower
3. same
4. depends upon the shape of body
5. none of the above.

lower

18. epending on the radiating properties, a body will be black when

1. p = 0, x = 0 and a = 1
2. p= l,T = 0anda = 0
3. p = 0, x = 1 and a = 0
4. x = 0, a + p = 0
5. a = 0,x + p= 1. where a = absorptivity, p == reflectivity, X = transmissivity.

p = 0, x = 0 and a = 1

19. epending on the radiating properties, a body will be opaque when

1. p = 0, x = 0 and a = 1
2. p=l,x = 0anda = 0
3. p = 0, x = 1 and a = 0
4. x - 0, a + p = 1
5. a=0,x + p= 1. where a = absorptivity, p = reflectivity, X = transmissivity.

x - 0, a + p = 1

20. epending on the radiating properties, a body will be white when

1. p = 0, x = 0 and a = 1
2. p=l,T = 0anda = 0
3. p = 0, x = 1 and a = 0
4. x = 0, a + p = 1
5. a = 0, x + p = 1. where a = absorptivity, p = reflectivity, x = transmissivity