101. The radiative heat transfer rate per unit area (W/m²) between two plane parallel gray surfaces (emissivity = 0.9) maintained at 400 K and 300 K is (σ = Stefan Boltzmann constant = 5.67 × 10^–8 W/m²K⁴)
     

1. 1. 992
      

   
   
   

   2. 812
      

   
   
   

   3. 464
      

   
   
   

   4. 567

   
   
   

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1. View Hint View Answer Discuss in Forum

   For plane surfaces
   

   Q	=	σ(T14 - T24)
   A		1	+	1	- 1
   		ε1		ε2

   
   Here , ε₁ = ε₂ = 0.9
   

   Q	=	5.67 × 10-8(4004 - 3004)
   A		1	+	1	- 1
   		0.9		0.9

   
   

   = 8 ∥ .84	w	≈ 812	w
   	m2		m2

   Correct Option: B

   For plane surfaces
   

   Q	=	σ(T14 - T24)
   A		1	+	1	- 1
   		ε1		ε2

   
   Here , ε₁ = ε₂ = 0.9
   

   Q	=	5.67 × 10-8(4004 - 3004)
   A		1	+	1	- 1
   		0.9		0.9

   
   

   = 8 ∥ .84	w	≈ 812	w
   	m2		m2

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102. For an opaque surface, the absorptivity (α), transmissivity (τ) and reflectivity ρ are related by the equation
     

1. 1. α + ρ = τ
      

   
   
   

   2. ρ + α + τ = 0
      

   
   
   

   3. α + ρ = 1
      

   
   
   

   4. α + ρ = 0

   
   
   

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1. View Hint View Answer Discuss in Forum

   α + τ + ρ = 1
   for opaque surface, τ = 0
   ∴ α + ρ = 1

   Correct Option: C

   α + τ + ρ = 1
   for opaque surface, τ = 0
   ∴ α + ρ = 1

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103. The following figure was generated from experimental data relating spectral black body emissive power to wave length at the three temperatures T₁, T₂ and T₃ (T₁ > T₂ >T₃).
     
     The conclusion in that the measurements are

1. 1. correct because the maxima in E_bλ show the correct trend
      

   
   
   

   2. correct because planck's law is satisfied
      

   
   
   

   3. wrong because the Stefan Boltzmann law in not satisfied
      

   
   
   

   4. wrong because Wien's displacement law is not satisfied
      

   
   
   

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1. View Hint View Answer Discuss in Forum

   Wien's displacement law is not satisfied, i.e., λ_max T = C
   which tells lower λ_max for higher temperature.

   Correct Option: D

   Wien's displacement law is not satisfied, i.e., λ_max T = C
   which tells lower λ_max for higher temperature.

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104. What is the value of the view factor for two inclined flat plates having common edge of equal length and wlth an angle of 20 degrees?
     

1. 1. 0.83
      

   
   
   

   2. 1.17
      

   
   
   

   3. 0.66
      

   
   
   

   4. 1.34

   
   
   

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1. View Hint View Answer Discuss in Forum

   F12 = F21 = 1 - sin		θ
   		2

   
   

   = 1 - sin		20°		= 0.826
   		2

   Correct Option: A

   F12 = F21 = 1 - sin		θ
   		2

   
   

   = 1 - sin		20°		= 0.826
   		2

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105. A diffuse radiation surface has
     

1. 1. Radiation intensity Independent of angle
      

   
   
   

   2. Emissive power Independent of angle
      

   
   
   

   3. Emissive power independent of wavelength
      

   
   
   

   4. Radiation intensity Independent of both angle and wavelength

   
   
   

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1. View Hint View Answer Discuss in Forum

   Radiation intensity is independent of angle in diffuse radiation.

   Correct Option: A

   Radiation intensity is independent of angle in diffuse radiation.

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