Dual Nature Of Radiation And Matter Ques 28
28. A $200 $ $W$ sodium street lamp emits yellow light of wavelength $0.6$ $ \mu m$. Assuming it to be $25 \%$ efficient in converting electrical energy to light, the number of photons of yellow light it emits per second is
[2012]
(a) $1.5 \times 10^{20}$
(b) $6 \times 10^{18}$
(c) $62 \times 10^{20}$
(d) $3 \times 10^{19}$
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Answer:
Correct Answer: 28.(a)
Solution:
- (a) Give that, only $25 \%$ of $200$ $ W$ converter electrical energy into light of yellow colour
$(\frac{h c}{\lambda}) \times N=200 \times \frac{25}{100}$
Where $N$ is the No. of photons emitted per second, $h=$ plank’s constant, $c$, speed of light.
$ \begin{aligned} & N=\frac{200 \times 25}{100} \times \frac{\lambda}{h c} \\ & =\frac{200 \times 25 \times 0.6 \times 10^{-6}}{100 \times 6.2 \times 10^{-34} \times 3 \times 10^{8}}=1.5 \times 10^{20} \end{aligned} $
BETA
