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GATE 2020 MT – Question 22

Transport Phenomena and Rate Processes · Heat transfer · 1 mark · Multiple choice

Select the correct log–log spectral-emission plots for a gray surface and a black body, both at 1000 K.

Diagram for GATE 2020 MT question 22
  1. Option A in the figure
  2. Option B in the figure
  3. Option C in the figure
  4. Option D in the figure

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Show answer and explanation

Correct answer: (D) Option D in the figure

Explanation

For a gray surface, emissivity ε is wavelength-independent and $E_{\lambda,g}=\epsilon E_{\lambda,b}$, with 0 < ε < 1. On logarithmic axes this is a constant downward vertical shift: the curves have identical shape and the same peak wavelength, with the gray curve always below the black curve. Graph D satisfies those conditions.

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