Write Enstein's photoelectric equation. State clearly the three salient features observed in photoelectric effect, which can be explained on the basis of the above equation.

Explanation

If a radiation photo of energy E=hv is incident on a photosensitive metal of work function `phi_(0)` then as per Einstein.s photoelectric equation, the maximum kinetic energy of the emitted photoelectron will be
`K_(max)=hv-phi_(0)`
The equation explains the three salient features observed in photoelectric effect, as explained below:
1. The maximum kinetic energy of photoelectron depends linearly on n and is independent of intensity of radiation. this has happened because in Einstein.s picture, photoelectric effect arises from the absorption of a single radiation photon by a single electron. the intensity of radiation is irrelevant to the basic process.
2. Since `K_(max)` must be non-negative, hence photoelectric emission is possible only if
`hv gt phi_(0)`
or if `v gt (phi_(0))/(h) or vgtv_(0)` where `v_(0)=(phi_(0))/(h)=`threshold frequency
Thus, there exists a threshold frequency for a metal surface, below which no photoelectric emission is possible, no matter how intense the incident radiation may be.
3. In Einstein.s picture intensity of radiation is proportional to the number of energy photons per unit area per unit time. the greater the number of radiation photons `(v gt v_(0))` available, the greater is the number of electrons coming out of metal.
Thus, for `vgtv_(0)`, the photoelectric current is proportional to intensity of incident radiation.