(a)(i)Threshold frequency- Threshold frequency is defined as the minimum frequency that is required for emission of electrons from a metal surface when electromagnetic radiation falls on the metal surface.
Stopping potential is the necessary potential applied externally to prevent the most energetic electron from reaching the endplate.
The starting point of both lines is from the same –ve potential that is also called as stopping potential and defined as the smallest magnitude of the anode potential which just stops photocurrent is called as stopping potential.
Work done by external voltage and this should be equal the Kinetic energy of electron which just fails to reach anode whose K.E will be given as
Where is the work function of metal.
Equating it we get
We can see the stopping potential doesn’t depend upon the intensity of light rather depends only on the wavelength of light and work function of the metal.
And saturation current for higher intensity of light is more as the number of photons falling on the metal plate per unit area increases, which consequently allows more electrons to escape escape from the metal surface
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