Dual Nature Of Light Question 409
Question: 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
Options:
A) $ 1.5\times 10^{20} $
B) $ 6\times 10^{18} $
C) $ 62\times 10^{20} $
D) $ 3\times 10^{19} $
Show Answer
Answer:
Correct Answer: A
Solution:
[a] Give that, only 25% of 200W converter electrical energy into light of yellow color $ ( \frac{hc}{\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. $ N=\frac{200\times 25}{100}\times \frac{\lambda }{hc} $ $ =\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} $
BETA
