A small metal plate (work-function Ws) is kept at a distance d from a singly ionised fixed ion. A monochromatic light beam is incident on the metal plate and photoelectric are emitted. The maximum wavelength of light so that the photo-electrons may
go round the ions along a circle is
 

• A

  $\frac{8{\mathrm{\pi \epsilon }}_0{\mathrm{W}}_0\mathrm{d}+{\mathrm{e}}^2}{8{\mathrm{\pi hc\epsilon }}_0\mathrm{d}}$

• B

  $\frac{8{\mathrm{\pi hc\epsilon }}_0\mathrm{d}}{8{\mathrm{\pi \epsilon }}_0{\mathrm{W}}_0\mathrm{d}+{\mathrm{e}}^2}$

• C

  $\frac{2\left(\frac{\mathrm{hc}}{{\mathrm{W}}_0}-{\mathrm{e}}^2\right)}{\mathrm{n}}$

• D

  $\frac{8{\mathrm{\pi \epsilon }}_0\mathrm{d}}{{\mathrm{hceW}}_0}$