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3 . Above threshold frequency the maximum kinetic energy of photo electrons depends upon the frequency of incident light .
4 . The photoelectric emission is an instantaneous process .
Einstein ’ s Photoelectric Equation
The maximum kinetic energy of photoelectrons
( E k ) max = hv – φ = h ( v – v o ) where v is frequency of incident light and v o is threshold frequency .
Stopping Potential
The minimum negative potential given to anode plate at which photoelectric current becomes zero is called stopping potential ( V o ).
Maximum kinetic energy of photo electrons ( E k ) max = 1 / 2 mv 2 max = eV o
Compton Effect
When a monochromatic beam of X – falls on a target containing free electrons . it is scattered . As a result , the electrons recoil and scattered radiation has wavelength longer than incident one . This effect is called Compton effect .
( i ) λ ’ – λ = λ = Compton shift Δλ = h / m o c ( 1 – cos φ ) where m o is rest mass of an electron and c is the speed of light h / m o c Compton shift Δλ is maximum , when φ = 180 °