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MCQs

Heat Radiation, Thermal Properties Of Matter, Dual Nature Of Matter

Total Questions : 247 | Page 6 of 25 pages
Question 51. The emissivity and the absorptivity of a real surface are equal for radiation with identical temperature and wavelength. This law is referred to as
  1.    Kirchhoff’s law
  2.    Lambert’s law
  3.    Planck’s law
  4.    Wein’s displacement law
 Discuss Question
Answer: Option A. -> Kirchhoff’s law
Answer: (a).Kirchhoff’s law
Question 52. The temperature of a solid surface changes from 27 K to 627 K. The emissive power changes would then confirm to the ratio
  1.    6:1
  2.    9:1
  3.    81:1
  4.    27:1
 Discuss Question
Answer: Option C. -> 81:1
Answer: (c).81:1
Question 53. Consider two bodies, one absolutely back and the other non-black and let these be at same temperature. Which one of the following statement is correct?
  1.    Black body radiates less intensively than a non-black body
  2.    Non-black body radiates less intensively than a black body
  3.    Both will radiates equally
  4.    None of them will radiates
 Discuss Question
Answer: Option B. -> Non-black body radiates less intensively than a black body
Answer: (b).Non-black body radiates less intensively than a black body
Question 54. If the temperature of a hot body is increased by 50%, the amount of radiations emitted by it would increase by nearly
  1.    200%
  2.    500%
  3.    50%
  4.    100%
 Discuss Question
Answer: Option B. -> 500%
Answer: (b).500%
Question 55. With an increase in wavelength, the monochromatic emissive power of a black body
  1.    Increases
  2.    Decreases
  3.    Decreases, reaches a minimum and then increases
  4.    Increases, reaches a maximum and then decreases
 Discuss Question
Answer: Option D. -> Increases, reaches a maximum and then decreases
Answer: (d).Increases, reaches a maximum and then decreases
Question 56. When Stefan-Boltzmann law is applied to a black body, it takes the form
  1.    E = σ T
  2.    E = σ T²
  3.    E = σ T³
  4.    E = σ T⁴
 Discuss Question
Answer: Option D. -> E = σ T⁴
Answer: (d).E = σ T⁴
Question 57. If a black body at 1000 K and a gray body at 1250 K emit the same amount of radiation, what should be the emissivity of the gray body?
  1.    0.3096
  2.    0.4096
  3.    0.5096
  4.    0.6096
 Discuss Question
Answer: Option B. -> 0.4096
Answer: (b).0.4096
Question 58. The radiant heat transfer from a plate of 2.5 cm² area at 1250 K to a very cold enclosure is 5.0 W. Determine the emissivity of the plate at this temperature
  1.    0.444
  2.    0.344
  3.    0.244
  4.    0.144
 Discuss Question
Answer: Option D. -> 0.144
Answer: (d).0.144
Question 59. The emissivity of the gray surface may be expressed as
  1.    σ /2 σb
  2.    σ / 3 σb
  3.    σ / σb
  4.    ½ σ / σb
 Discuss Question
Answer: Option C. -> σ / σb
Answer: (c).σ / σb
Question 60. When the emissivity of non-black surface is constant at all temperatures and throughout the entire range of wavelength, the surface is called
  1.    Gray body
  2.    Transparent body
  3.    Opaque bodies
  4.    Perfect black body
 Discuss Question
Answer: Option A. -> Gray body
Answer: (a).Gray body

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