Question

Good emitters are good absorbers is a statement concluded from

• A. Newtons law of cooling
• B. Stefans law of radiation
• C. Provosts theory
• D. Kirchhoffs law

Answer 1

Answer: (D)

Kirchhoffs law

Answer 2

According to Kirchhoffs law the ratio of emissive power to absorptive power is same for all surfaces at the same temperature and is equal to the emissive power of a perfectly black body at that temperature. Hence, $\frac{e_{1}}{a_{1}}=\frac{e_{2}}{a_{2}}=\ldots\left[\frac{E}{A}\right]_{\text {perfectly black body }}$ Now, since $\left(E_{\lambda}\right)_{\text {black }}$ is constant at a given temperature, this implies that good absorber is a good emitter (or radiator).