When a photon of suitable frequency is incident on a metal surface, a photoelectron is emitted from it. If the frequency is below a threshold frequency (ν0) for the surface, no photoelectron is emitted. For a photon of frequency ν (ν > ν0), the kinetic energy of the emitted photoelectron is:
Km = h(ν − ν0)
The photocurrent can be stopped by applying a potential V0, called the "stopping potential," on the anode. Thus, the maximum kinetic energy of photoelectrons is:
Km = eV0 = h(ν − ν0)
The experimental graph between V0 and ν for a metal is shown in the figure. This is a straight line of slope m.
