How many photons of a radiation of wavelength λ=5×10−7 m must fall per second on a blackened plate in order to produce a force of 6.62×10−5N?
A
3×1019
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B
5×1022
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C
2×1022
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D
1.67×1018
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Solution
The correct option is B5×1022 Momentum of photon is given by,
p=hλ
Momentum of n photons, =nhλ
Force is the change in momentum. Since, the plate is blackened, all the photons are being absorbed. Thus, change in momentum and hence the force is given by