Thermal Properties Of Matter Ques 7
7. A black body is at a temperature of $5760 K$. The energy of radiation emitted by the body at wavelength $250 nm$ is $U_1$, at wavelength 500 $nm$ is $U_2$ and that at $1000 nm$ is $U_3$. Wien’s constant, $b=2.88 \times 10^{6} nmK$. Which of the following is correct?
[2016]
(a) $U_1=0$
(b) $U_3=0$
(c) $U_1>U_2$
(d) $U_2>U_1$
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Answer:
Correct Answer: 7.(d)
Solution:
- (d) According to Wien’s displacement law, maximum wavelength of emitted radiation corresponds to $\lambda_m=\frac{b}{T}$
$ \lambda_m=\frac{2.88 \times 10^{6} nmK}{5760 K}=500 nm $
From the graph $U_1<U_2<U_3$
At a given temperature, intensity of heat radiation decreases with wavelength, reaches a maximum at a particular wavelength and with further increase in wavelength it decreases.
BETA
