Question

A parallel beam of light is incident normally on a perfectly absorbing surface. If the force exerted by the light beam on the surface is 2 x 10^-7 N in 10 nanoseconds, the energy of photons hitting the surface is ____________.

Options

• 600 nJ

• 500 nJ

• 400 nJ

• 700 nJ

Answer 1

A parallel beam of light is incident normally on a perfectly absorbing surface. If the force exerted by the light beam on the surface is 2 x 10^-7 N in 10 nanoseconds, the energy of photons hitting the surface is 600 nJ.

Explanation:

Power oftbe incident photons is,

`"P" = "E"/"t"`

But, P = Fc

`therefore "E" = "Fct"`

`= 2 xx 10^-7 xx 3 xx 10^8 xx 10 xx 10^-9`

`= 600 xx 10^-9  "J"`

`= 600  "nJ"`