When light of wavelength $\lambda$ is incident on a photosensitive surface,photons of power $P$ are emitted. The number of photons $n$ emitted in time $t$ is: [$h$ = Planck's constant,$c$ = velocity of light in vacuum]

• A
  $\frac{hc}{P \lambda t}$
• B
  $\frac{P \lambda}{htc}$
• C
  $\frac{P \lambda t}{hc}$
• D
  $\frac{hP}{\lambda tc}$