The GATE Grind

GATE 2023 CH – Question 30

Heat Transfer · Radiation · 1 mark · Multiple select

Given that $E$ (in W m$^{-2}$) is the total hemispherical emissive power of a surface maintained at a certain temperature, which of the following statements is/are CORRECT?

  1. $E$ does not depend on the direction of the emission.
  2. $E$ depends on the viewfactor.
  3. $E$ depends on the wavelength of the emission.
  4. $E$ does not depend on the frequency of the emission.

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Show answer and explanation

Correct answer: (A) $E$ does not depend on the direction of the emission.; (D) $E$ does not depend on the frequency of the emission.

Explanation

The total hemispherical emissive power is the radiation integrated over all directions in the hemisphere and over all wavelengths (frequencies), so it depends on neither the direction (A) nor the wavelength or frequency (D, C is false). The view factor describes the exchange between two surfaces and is not part of the emissive power of one surface (B is false).