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A beam of light of wavelength lambda is ...

A beam of light of wavelength `lambda` is totally reflected at normal incidence by a plane mirror . The intensity of the light is such that photons hit the mirror . The intensity of the light is such that photons hit the mirror at a rote `n` . Given that the Planck constant is `h` , the force exerted on the mirror by this beam is

A

`nh lambda`

B

`nh//lambda`

C

`2nh//lambda`

D

`2nlambda//h`

Text Solution

Verified by Experts

The correct Answer is:
D
Let `p` be the momentum of a photon arriving at the mirror , we then have `p = (h)/(lambda)`
The change in momentum for a photon
`= p - (- p) = 2 p = ( 2h)/( lambda)`
Force = rate of change of momentum of the photons
` = n ((2h)/(lambda))` , where `n` is the rate at which the photons hitting the mirror .
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Knowledge Check

  • A ray of light of wavelength lambda is incident on mirror at an angle of incidence 60^(@) . The wavelength of light after reflection will be

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    D
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