If the work function of a metal is ′ϕ′ and the frequency of the incident light is 'v', there is no emission of photoelectron if
v<ϕh
v=ϕh
v>ϕh
v>=<ϕh
For no emission of photoelectron, energy of incident light < Work function ⇒hv<ϕ⇒v<ϕh