A bulb emits light of wavelength 1987 8 7.nm. The bulb is rated as 200 W and 14% of the energy is em

Question

A bulb emits light of wavelength 1987 8 7.nm. The bulb is rated as 200 W and 14% of the energy is emitted as light. How many photons are emitted by the bulb per second?

Accepted Answer

$p = \frac{E}{t} = \frac{n.hc}{t.\lambda}$

$\Rightarrow \frac{14}{100} \times 200 = \frac{n \times 6.626 \times 10^{- 34} \times 3 \times 10^{8}}{1 \times \frac{1987.8}{7} \times 10^{- 9}} $$$\therefore n = 4 \times 10^{19}\text{ }\text{s}^{- 1}$$

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