Heat Transfer

11. According of Kirchhoff's law,

1. radiant heat is proportional to fourth power of absolute temperature
2. emissive power depends on temperature
3. emissive power and absorptivity are constant for all bodies
4. ratio of emissive power to absorptive power is maximum for perfectly black body
5. ratio of emissive power to absorptive power for all bodies is same and is equal to the emissive power of a perfectly black body.

View answer

12. According 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.

View answer

13. According to Prevost theory of heat exchange

1. it is impossible to transfer heat from low temperature source to t high temperature source
2. heat transfer by radiation requires no medium
3. all bodies above absolute zero emit radiation
4. heat transfer in most of the cases takes place by combination of conduction, convection and radiation
5. rate of heat transfer depends on thermal conductivity and temperature difference.

View answer

14. According 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.

View answer

15. According 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.

View answer

16. According 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.

View answer

17. All radiations in a black body are

1. reflected
2. refracted
3. transmitted
4. absorbed
5. partly reflected and partly absorbed.

View answer

18. 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.

View answer

19. Depending 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.

View answer

20. Depending 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.

View answer