A 124 W bulb converts only 15% of the energy supplied to it into visible light of wavelength 640 nm. How many photons are emitted by the light bulb in one second ?

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$6 \times 10^{19}$

$8 \times 10^{18}$

$3 \times 10^{19}$

$4 \times 10^{19}$

answer is B.

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Detailed Solution

The number of protons can be calculated as;

$\begin{array}{l} 124 \times 0.15 \times 1 \\ = N \times \frac{1240}{640} \times 1.6 \times 10^{- 19} \\ \Rightarrow N = 6 \times 10^{19} \end{array}$

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