When light of wavelength ' $\lambda$ ' is incident on photosensitive surface, photons of power 'P' are…
When light of wavelength ' $\lambda$ ' is incident on photosensitive surface, photons of power
'P' are emitted. The number of photons (n) emitted in 't' second is
(h= Planck's constant, $\mathrm{c}=$ velocity of light in vacuum)
$\frac{h \mathrm{C}}{\mathrm{P} \lambda t}$
$\frac{P \lambda t}{h_{C}}$
$\frac{\mathrm{P} \lambda}{\operatorname{htc}}$
$\frac{h \mathrm{P}}{\lambda t \mathbf{C}}$
Solution
Energy of each photon $=\frac{h c}{\lambda}$
If $n$ photons are emitted in time $t$ then the energy emitted in time $t$ is $\frac{\text { nhc }}{\lambda}$
$\begin{aligned} \text { Power P } &=\text { Energy emitted per second } \\ &=\frac{\mathrm{nhc}}{\lambda \mathrm{t}} \\ \therefore \mathrm{n} &=\frac{\mathrm{P} \lambda \mathrm{t}}{\mathrm{hc}} \end{aligned}$
.