GATE 2026 Chemical Engineering, Q13 · Heat Transfer
The correct answer is A, absorptivity of the body at the same wavelength.
Question
A body is placed inside a perfectly black enclosure and is allowed to reach thermal equilibrium. According to the Kirchhoff's identity, which one of the following is equal to the emissivity of the body at a given wavelength?
Official answer: absorptivity of the body at the same wavelength
Why
GATE 2026 official key: (A). Kirchhoff's law: at thermal equilibrium, a body's emissivity equals its absorptivity at the same wavelength.
Explanation cross-checked for consistency. Final answer matches the official IIT answer key.