Transmission Of Heat Question 150
Question: If between wavelength $ \lambda $ and $ \lambda +d\lambda $ , $ {e _{\lambda }} $ and $ {a _{\lambda }} $ be the emissive and absorptive powers of a body and $ {E _{\lambda }} $ be the emissive power of a perfectly black body, then according to Kirchoff’s law, which is true
[RPMT 1998; MP PET 1991]
Options:
A) $ {e _{\lambda }}={a _{\lambda }}={E _{\lambda }} $
B) $ {e _{\lambda }}{E _{\lambda }}={a _{\lambda }} $
C) $ {e _{\lambda }}={a _{\lambda }}{E _{\lambda }} $
D) $ {e _{\lambda }}{a _{\lambda }}{E _{\lambda }} $ = constant
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Answer:
Correct Answer: C
Solution:
According to Kirchoff’s law, the ratio of emissive power to absorptive power is same for all bodies is equal to the emissive power of a perfectly black body i.e.,
$ {( \frac{e}{a} ) _{\text{body}}}$=
${E _{\text{Black},\text{body}}} $
for a particular wave length
$ {{( \frac{e _{\lambda}}{a _{\lambda }} )} _{\text{body}}}$=
${{({E _{\lambda }})} _{\text{Black},text{body}}} $
Therefore $ {e _{\lambda }}={a _{\lambda }}{E _{\lambda }} $
BETA
