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  • A 200 W sodium street lamp emits yellow light of wavelength 0.6 m. Assuming it to be 25% efficient in converting electric

A 200 W sodium street lamp emits yellow light of wavelength 0.6 \mum. Assuming it to be 25% efficient in converting electrical energy to light, the number of photons of yellow light it emits per second is:

Option: 1

1.5 x 1020


Option: 2

6 x1018


Option: 3

62 x 1020


Option: 4

3 x 1019


Answers (1)

best_answer

Amount of light energy produced 

= 50 W. (25% of 200 W)

Since P = N \frac{hc}{\lambda }. (\lambda = 600 nm = 600\times 10^{-9})

N=\frac{P\lambda }{hc} = \frac{200\times 600\times 10^{-9}}{6.62\times 10^{-34}\times 3\times 10^{8}}\times 0.25

N = \frac{3\times 10^{-5}}{19.86\times 10^{-26}} = 1.5\times 10^{20}

N = 1.5\times 10^{20} per second

 

Posted by

Divya Prakash Singh

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