Module 5 : MODERN PHYSICS
Lecture 24 : Photoelectric Effect
 
If the voltage is reversed making the anode negative with respect to the cathode, the electrons get decelerated and only the more energetic of the electrons can reach the anode.
 
\includegraphics{fig4.7.eps}
  If the reverse voltage is such that even the electrons which are ejected with the maximum kinetic energy cannot overcome the potential, the photo-current becomes zero. The reverse voltage which is just enough to stop the most energetic photoelectrons is called the stopping potential. If $ K_{max}$ is the maximum kinetic energy of the electrons, the stopping potential is $ V_s$ defined by
 
$\displaystyle eV_s = K_{max}$
 
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