(a) Write Einstein's photoelectric equation. State clearly how this equation is obtained using the photon picture of electromagnetic radiation.
(b) Write the three salient features observed in photoelectric effect which can be explained using this equation.

Explanation

(a) To Explain photoelectric emission, Einstein assumed that emission of a photoelectron was the result of interaction of a single incident photon with a stationary electron present in metal surface, in which photon is completely absorbed by the electron. we know that to remove the electron, a minimum energy `phi_(0)` (known as work function of given metal) is required. thus, when a photon of energy E=hv is absorbed by an electron, an energy `phi_(0)` (provided that `hvgt phi_(0)`) is used up in liberating the electron and balance energy appears as kinetic energy `K_(max)` of ejected photo electron.
`therefore hv=phi_(0)+K_(max)` . . (i)
If we go on reducing v then for a certain frequency`v_(0)` (known as threshold frequency) `K_(max)` becomes just equal to zero. then
`hv_(0)=phi_(0)`
Combining the two results, we obtain `hv=hv_(0)+K_(max)`.
`implies h(v-v_(0))=K_(max)=(1)/(2)mv_(max)^(2)` . . (ii)
if `V_(0)` be the stopping potential, then `K_(max)=eV_(0)` and hence, we have
`h(v-v_(0))=eV_(0)`
Equation written either as (i) or (ii) or (iii) is known as Einstein.s photoelectric equation.