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Question
How many photons per second emanate from a 50 mW laser of 640 nm?
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Solution
P = 50 mW
λ = 640 nm
h = 6.6 × 10−34 Js
c = 3 × 108 ms−1
Number of photons emanate per second np = `"P"/"E" = ("P"λ)/"hc"`
= `(50 xx 10^-3 xx 640 xx 10^-9)/(6.6 xx 10^-34 xx 3 xx 10^8)`
= `(32000 xx 10^(-6))/(19.8 xx 10^(-26))`
= 1616.16 × 1017
np = 1.61 × 101017 s−1
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