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  4. The number of photons of wavelength of 540 nm emitted per second by an electric bulb of power 100 W is (Given h = 6 × 10-34 J s)

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Q. The number of photons of wavelength of 540 nm emitted per second by an electric bulb of power 100 W is (Given $h = 6 \times 10^{-34} \,J \, s)$

JIPMERJIPMER 2012Dual Nature of Radiation and Matter

Solution:

Power = $\frac{nhc}{\lambda}$
$\Rightarrow \:\: 100 = \frac{n \times ( 6 \times 10^{-34} )(3 \times 10^8)}{540 \times 10^{-9}}$
$\Rightarrow \:\:\: n = \frac{ 100 \times 540 \times 10^{-9}}{18 \times 10^{-26}} = 3 \times 10^{20}$