Question

Which statement best represents Kirchhoff's Law of Thermal Radiation?

• A. Good absorbers are poor emitters of radiation
• B. All bodies emit radiation equally regardless of material
• C. Radiation intensity depends only on temperature
• D. Emissivity of a body equals its absorptivity at thermal equilibrium

Hint:

Remember Kirchhoff's Law: \[ \boxed{\varepsilon=\alpha} \] Good absorbers are also good emitters.

Answer 1

The Correct Option is D

Concept: Kirchhoff's Law of Thermal Radiation states that for a body in thermal equilibrium, the emissivity is equal to the absorptivity at the same wavelength and temperature.

Step 1: State the law. \[ \boxed{\varepsilon=\alpha} \] where
• \(\varepsilon\) = emissivity
• \(\alpha\) = absorptivity

Step 2: Identify the correct statement. Therefore, \[ \boxed{\text{Emissivity equals absorptivity at thermal equilibrium}.} \] Hence, the correct option is \[ \boxed{(D).} \]