Work function of lithium and copper are respectively 2.3 eV and 4.0 eV. Which metal will be useful for the photoelectric cell working with visible light? (h=6.6×10−34Js,c=3×108m/s

From λ0=12375W0The maximum wavelength of light required for the photoelectron emission, λ0Li=123752.3=5380Å Similarly λ0Cu=123754=3094ÅThe wavelength 3094Å does not lie in the visible region, but it is in the ultraviolet region. Hence to work with visible light, lithium metal will be used for photoelectric cell.