Kmax​=λhc​−ϕKinetic energy of electron reaching the anode will beK=λph​hc​−ϕ+eVλe​=2mK​h​=2m(λph​hc​−ϕ+eV)​h​​If eV≫ϕ then, λc​=2m(λph​hc​+eV)​h​If Vf​=4Vi​ then, (λe​)f​=2(λe​)i​​