NEET Physics Notes Optics- Photoelectric Effect -Photon
In interaction of radiation with matter, radiation behaves as if it is made up of particles called photons. Each photon travels in vacuum (or air) with a constant speed c the speed of light, having a value c = 3 x 108ms_1. This speed does not depend on frequency or energy/momentum of photon or on relative motion of source and observer, etc.
Energy of photons of frequency v or wavelength X is given by
Photoelectric effect is the phenomenon of emission of electrons (known as photoelectrons) from the surface of metals when light radiation of suitable frequency are incident on them.
For a given metal, there exists a certain minimum frequency of light radiation below which no photoelectric emission takes place. This minimum frequency of radiation is known as the threshold frequency(v0 ).
The minimum energy of incident radiation needed to eject the electrons from metal surface is known as work function Φ0 of that surface. Work function is related to Φ0
threshold frequency as
where, X 0 = threshold wavelength
For photo emission to take place energy of incident light (F) is related as,
According to Einstein’s photoelectric
If in a photoelectric tube we apply a negative potential, then for a certain minimum negative potential the photoelectric current becomes zero.
This negative potential is known as stopping potential It is thus, a measure maximum kinetic energy of photoelectrons,