Heat Transfer Questions and Answers – Kirchoff’s Law

This set of Heat Transfer Multiple Choice Questions & Answers (MCQs) focuses on “Kirchoff’s Law”.

1. If radiant energy E _B emitted by the black surface strikes the non-black surface. If non-black surface has absorptivity α, it will absorb how much radiations?
a) α E _B
b) 2 α E _B
c) 3 α E _B
d) 4 α E _B
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2. If two surfaces are at the same temperature, then the conditions correspond to mobile thermal equilibrium for which the resultant interchange of heat is zero are
a) 3 E – α E _B = 0
b) 2 E – α E _B = 0
c) E – α E _B = 0
d) ½ E – α E _B = 0
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3. The absorptivity of black body equals to
a) 2
b) 1
c) 3
d) 4
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4. A diathermanous body
a) Shines as a result of incident radiation
b) Gets heated up a result of absorption of incident radiation
c) Allows all the incident radiation to pass through it
d) Partly absorbs and partly reflects the incident radiation
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5. Choose the false statement
a) Snow is nearly black to thermal radiation
b) Absorption of radiation occurs in a very thin layer of material near the surface
c) Transmissivity varies with the wavelength of incident radiation
d) Most of the engineering materials have rough surfaces, and these rough surfaces give regular (specular) reflections
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6. The emissivity and the absorptivity of a real surface are equal for radiation with identical temperature and wavelength. This law is referred to as
a) Kirchhoff’s law
b) Lambert’s law
c) Planck’s law
d) Wein’s displacement law
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7. With an increase in wavelength, the monochromatic emissive power of a black body
a) Increases
b) Decreases
c) Decreases, reaches a minimum and then increases
d) Increases, reaches a maximum and then decreases
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8. The temperature of a solid surface changes from 27 K to 627 K. The emissive power changes would then confirm to the ratio
a) 6:1
b) 9:1
c) 81:1
d) 27:1
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9. If the temperature of a hot body is increased by 50%, the amount of radiations emitted by it would increase by nearly
a) 200%
b) 500%
c) 50%
d) 100%
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10. Consider two surfaces, one absolutely black and the other non-black. These surfaces are arranged parallel to each other and so close that the radiation of one falls totally on the other. Choose the correct option

a) 1 denotes the radiant energy E emitted by the non-black surface impinges on the black surface
b) 1 denotes the radiant energy E emitted by the black surface impinges on the non-black surface
c) 2 and 3 denotes the quantity α E _b
d) 4 denotes the quantity (1 – α) E _b
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Sanfoundry Global Education & Learning Series – Heat Transfer.

To practice all areas of Heat Transfer, here is complete set of 1000+ Multiple Choice Questions and Answers.