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MCQs

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

Total Questions : 247 | Page 18 of 25 pages
Question 171. Which one is true for opaque body?
  1.    Transmissivity is zero
  2.    Reflectivity is zero
  3.    Absorptivity is zero
  4.    Reflectivity is unity
 Discuss Question
Answer: Option A. -> Transmissivity is zero
Answer: (a).Transmissivity is zero
Question 172. Energy strikes a vertical hemispherical plate with an intensity of 640 W/m². The absorptivity is thrice the transmissivity and twice the reflectivity. Determine the rate of transmission
  1.    236.74 W/m²
  2.    116.37 W/m²
  3.    187.87 W/m²
  4.    456.09 W/m²
 Discuss Question
Answer: Option B. -> 116.37 W/m²
Answer: (b).116.37 W/m²
Question 173. The absorptivity of a surface depends upon
(i) Direction of reflected radiation
(ii) Temperature of the surface
(iii) Composition
Identify the correct statements
  1.    1, 2 and 3
  2.    1 and 3
  3.    2 only
  4.    2 and 3
 Discuss Question
Answer: Option D. -> 2 and 3
Answer: (d).2 and 3
Question 174. A body that reflects all the incident thermal radiations is called a
  1.    Opaque body
  2.    Gases
  3.    Black body
  4.    Specular body
 Discuss Question
Answer: Option D. -> Specular body
Answer: (d).Specular body
Question 175. What is the absorptivity of gray body?
  1.    Below unity
  2.    Unity
  3.    2
  4.    2.5
 Discuss Question
Answer: Option A. -> Below unity
Answer: (a).Below unity
Question 176. Let 220 W/m² of radiant energy is absorbed by a convex surface, 90 W/m² is reflected and 40 W/m² is transmitted through it. What is the value of absorptivity?
  1.    0.72
  2.    0.62
  3.    0.52
  4.    0.42
 Discuss Question
Answer: Option B. -> 0.62
Answer: (b).0.62
Question 177. Energy strikes a vertical hemispherical plate with an intensity of 640 W/m². The absorptivity is thrice the transmissivity and twice the reflectivity. Determine the rate of absorption
  1.    449.12 W/m²
  2.    349.12 W/m²
  3.    249.12 W/m²
  4.    149.12 W/m²
 Discuss Question
Answer: Option B. -> 349.12 W/m²
Answer: (b).349.12 W/m²
Question 178. For a grey surface
  1.    Reflectivity equals emissivity
  2.    Emissivity equals transmissivity
  3.    Absorptivity equals reflectivity
  4.    Emissivity is constant
 Discuss Question
Answer: Option D. -> Emissivity is constant
Answer: (d).Emissivity is constant
Question 179. Absorptivity of a body is equal to its emissivity
  1.    Under thermal equilibrium conditions
  2.    For a polished surface
  3.    At one particular temperature
  4.    At shorter wavelengths
 Discuss Question
Answer: Option A. -> Under thermal equilibrium conditions
Answer: (a).Under thermal equilibrium conditions
Question 180. Electromagnetic waves strikes a hot body maintained at 900 degree Celsius which has a reflectivity of 0.66 and a transmissivity of 0.022. Let the absorbed flux be 60 W/m². Determine the rate of incident flux
  1.    168.67 W/m²
  2.    178.67 W/m²
  3.    188.67 W/m²
  4.    198.67 W/m²
 Discuss Question
Answer: Option C. -> 188.67 W/m²
Answer: (c).188.67 W/m²

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