Example 4. (a) The work function for the surface of aluminiu a) The work function for the surface of aluminium is 4.2 eV. How much potential difference will be required to stop the emission of maximum energy electrons emitted by night emitted by light of 2000 À wavelength ? (b) What will be the wavelength of that incident light for which stopping potential ident light for which stopping potential will be zero ? h = 6*6 x 10-34 Js, c = 3 x 108 ms-1. Solution. (a) Here, do = 4.2 eV = 4.2 x 1.6 X 10-19 J. V=2.1= 2000 Å = 2000 x 10-10 m