Dual Nature Of Radiation

In a photoelectric experiment ultraviolet light of wavelength 280 nm is used with lithium cathode having work function \(\phi\) = 2.5 eV. If the wavelength of incident light is switched to 400 nm, find out the change in the stopping potential. (h = 6.63 \(\times\) 10^\(-\)34 Js, c = 3 \(\times\) 10⁸ ms^\(-\)1)