A monochromatic source having wavelength 2480A0 is used to irradiate a metallic sphere of radius 2 m and work function 3eV. If the emission of photoelectrion  is stopped after sometime then charge on the sphere at that instant is

energy of the incident photon is 124002480=5 eVwork function 3 eV. so according to Einstein's equation  hν=W+ eVs      eVs= 2eV  stopping potential will be  2V  when the potential of the sphere becomes 2 V electron emission is stopped   potential of the sphere   V=q4πε0r=2 V   q =8πεr=16πε0