write einstein’s photoelectric equation. state clearly …

Einstein’s photoelectric equation,

 K_max​=hν−ϕ0​ where

Kmax​ is the max kinetic energy of emitted electrons and ϕ0​ is the work function.

According to Planck’s quantum theory, light radiations consist of small packets of energy. Einstein postulated that a photon of energy hv is absorbed by the electron of the metal surface, then the energy is used to liberate electron from the surface and rest of the energy becomes the kinetic energy of the electron.

Energy of photon is,

E=hv

Where,  h = Planck’s constant

v = frequency of light

The minimum energy required by the electron of a material to escape out of it, is work function.

The additional energy acquired by the electron appears as the maximum kinetic energy ‘K_max’ of the electron.

Einstein's photoelectric equation

K_max​=eVo​

Salient features observed in photoelectric effect: —

The stopping potential and hence the maximum kinetic energy of emitted electrons varies linearly with the frequency of incident radiation.

There exists a minimum cut - off frequency , for which the stopping potential is zero.

Photoelectric emission is instantaneous.

Einstein's photoelectric equation is E_k = hv -W for a single photon ejecting a single electron. 

(i) Explanation of frequency law: When frequency of incident photon (v), increases, the kinetic energy of emitted electron increases. Intensity has no effect on kinetic energy of photoelectrons.

(ii) Explanation of intensity law: When intensity of incident light increases, the number of incident photons increases, as one photon ejects one electron; the increase in intensity will increase the number of ejected electrons. In other words, photocurrent will increase with increase of intensity. Frequency has no effect on photocurrent. 

(iii) Explanation of no time lag law: When the energy of incident photon is greater than work function, the photoelectron is immediately ejected. Thus there is no time lag between incidence of light and emission of photoelectrons.c