The figure shows the variation of photo-current with anode potential for a photo-sensitive surface for three different radiations. Let ${\mathrm{I}}_{\mathrm{a}},{\mathrm{I}}_{\mathrm{b}}\mathrm{and}{\mathrm{I}}_{\mathrm{c}}$ be the intensities and ${\mathrm{f}}_{\mathrm{a}},{\mathrm{f}}_{\mathrm{b}}\mathrm{and}{\mathrm{f}}_{\mathrm{c}}$ be the frequencies for the curves a. b and c respectively

• A

  ${\mathrm{f}}_{\mathrm{a}}={\mathrm{f}}_{\mathrm{b}}\mathrm{and}{\mathrm{l}}_{\mathrm{a}}\ne {\mathrm{l}}_{\mathrm{b}}$

• B

  ${\mathrm{f}}_{\mathrm{a}}={\mathrm{f}}_{\mathrm{b}}\mathrm{and}{\mathrm{l}}_{\mathrm{a}}={\mathrm{l}}_{\mathrm{c}}$

• C

  ${\mathrm{f}}_{\mathrm{a}}={\mathrm{f}}_{\mathrm{b}}\mathrm{and}{\mathrm{l}}_{\mathrm{a}}={\mathrm{l}}_{\mathrm{b}}$

• D

  ${\mathrm{f}}_{\mathrm{a}}={\mathrm{f}}_{\mathrm{b}}\mathrm{and}{\mathrm{l}}_{\mathrm{a}}\ne {\mathrm{l}}_{\mathrm{c}}$