When light falls on metal electrons are emitted from the surface of the metal. This phenomena is termed as photo electric effect. The energy the impinging photons (light consists of tiny mass less particles called photons which carry energy of h*v where h is Planck’s constant and v is frequency of light) should be at least equal to work function (characteristic property of metal). If the impinging photon on metal is having energy greater than the work function of metal the extra energy will appear as kinetic energy of ejected electron. Accordingly we can write
h*v = Wf + K.E
Where Wf is the work function of metal, K.E is the kinetic energy of ejected electron.