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  • A modern watt sodium street lamp emits yellow light of wavelength <img alt="0.6\mu m" src="https://entrancecorner.oncodec

A modern 200 watt sodium street lamp emits yellow light of wavelength 0.6\mu m. Assuming it to be 25% efficient in converting electrical energy to light, number of photons of yellow light it emits per second is -

Option: 1

6.2\times 10^{20}


Option: 2

3\times10^{19}


Option: 3

1.5\times10^{20}


Option: 4

6\times10^{18}


Answers (1)

best_answer

\begin{aligned} \frac{\mathrm{n}}{\mathrm{t}} & =\frac{\mathrm{IA}}{\mathrm{h} \nu}=\frac{\mathrm{IA} \lambda}{\mathrm{hc}}=\frac{\mathrm{W} \lambda}{\mathrm{hc}} \\ & =\frac{50 \times 6 \times 10^{-7}}{6.6 \times 10^{-34} \times 3 \times 10^8} \\ & =\frac{300}{20} \times 10^{19} \\ & =1.5 \times 10^{20} \end{aligned}

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Shailly goel

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