NEET Physics Notes Optics- Photoelectric Effect -Effect of Intensity on Photoelectric Emision
Effect of Intensity on Photoelectric Emision
For a light of given frequency v > v0 (or given wavelength λ < λ0 number of photoelectrons and consequently the photoelectric current I increases.However, the stopping potential v0 (i.e. the maximum kinetic energy Kmax of photoelectrons) unchanged.
Effect of Frequency on Photoelectric Emission
If keeping the intensity of incident light constant, the frequency of incident light , is increased, then the stopping potential V0 (and hence, Kmax ) increases but the photoelectric current I remains unchanged.
A photon may collide with a material particle. The total energy and the total momentum remain conserved in such a collision. Photoelectric emission is an instantaneous phenomenon.
Time lag between the incidence of light photon and emission of photoelectron is of the order of 10_9s
Variation of stopping potential V0 with frequency v of incident radiation is as shown in above figure.
Laws of Photoelectric Emission Effect
- Lenard and Millikan gave the following laws on the basis of experiments on photoelectric effect.
- The rate of emission of photoelectrons from the surface of a metal varies directly as the intensity of the incident light falling on the surface.
- The maximum kinetic energy of the emitted photoelectrons is independent of the intensity of the incident light.
- The maximum kinetic energy of the photoelectrons increases linearly with increase in the frequency of the incident light.
- As soon as, the light is incident on the surface of the metal, the photoelectrons are emitted instantly, i.e. there is no time lag between incidence of light and emission of electrons.
Energy and Momentum of Photon From Einstein’s mass-energy relation