Explain the term stopping potential and threshold frequency.

Explanation

Stopping potential. It is minimum negative potential given to the anode in a photocell for which the photoelectric current becomes zero. If `V_0` is the stopping potential, then maximum K.E. of emitted photoelectron is
`(K.E.)_(max)=eV_0=hv-phi_0 :. V_0=(hv)/e-(phi_0)/e`
Threshold frequency. It is the minimum frequency of the incident radiation for which just emission of photoelectrons takes place from a metal surface without any K.E. If `v_0` is the threshold frequency, then using Einstein's photoelectric equation
`0=hv_0-phi_0 or v_0=(phi_0)/h`