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Question
What is the number of photons of light with a wavelength of 4000 pm that provide 1 J of energy?
Solution
Energy (E) of a photon = hν
Energy (En) of ‘n’ photons = nhν
`=> n = ("E"_nlambda)/(hc)`
Where,
λ = wavelength of light = 4000 pm = 4000 ×10–12 m
c = velocity of light in vacuum = 3 × 108 m/s
h = Planck’s constant = 6.626 × 10–34 Js
Substituting the values in the given expression of n:
`"n" = ((1)xx(4000xx10^(-12)))/((6.626xx10^(-34))(3 xx 10^8)) = 2.012 xx 10^(16)`
Hence, the number of photons with a wavelength of 4000 pm and energy of 1 J are 2.012 × 1016
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