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Question
A 150 W lamp emits light of the mean wavelength of 5500 Å. If the efficiency is 12%, find out the number of photons emitted by the lamp in one second.
Solution
P = 150 W
λ = 5500 × 10−10 m
Efficiency = 12%
N = `("P"λ)/"hc"`
= `(150 xx 5500 xx 10^-10)/(6.626 xx 10^-34 xx 3 xx 10^8)`
= `(825 xx 10^-7)/(19.878 xx 10^-26)`
= 41.5 × 1019
Number of photons emitted is with 12% efficiency = `41.5 xx 10^19 xx 12/100`
N = 4.98 × 1019
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