Radiation of wavelength `5000 A^@` incidents on a metal surface to just cause photo emission. Calculate the work function of the metal.

The velocity of photoelectrons is 10^6 ms^-1 when light of wavelength 6000 A^@ falls on a metal surface. Calculate the work function of the metal.

The velocity of photoelectrons is 10^6 m//s when light of 4000A^@ falls on the metal surface. Calculate the work function of the metal.