when a point light source, of power P emitting monochromatic light of wavelength$\lambda$ is kept at a distance $\alpha$ from a photo-sensitive surface of work-function W₀ and area A which of the expressions is wrong 

• A

   number of photons striking the surface per unit time as $\mathrm{P\lambda A}/4{\mathrm{\pi cha}}^2$

• B

  the stopping potential needed to stop the most energetic emitted photo-electrons as $\left(\mathrm{hc}-{\mathrm{\lambda W}}_0\right)/\mathrm{\lambda e}$

• C

  $\text{ photo emission only if }\mathrm{\lambda }\text{ lies in the range }0\le \mathrm{\lambda }\le \mathrm{hc}/{\mathrm{W}}_0$

• D

  none