Photoelectric effect cannot be explained on the basis of wave theory of light". Explain this statement.
Photoelectric effect cannot be explained on the basis of wave theory of light because of the following reasons:
[(i)] As per wave theory of light}, the electric field component ($E$) of light increases with the increase in the intensity of the light. When light falls on a metal surface, the force acting on a free electron in the metal surface increases with the increase in the intensity of the incident light ($F = -eE$). As a result of this, the kinetic energy acquired by the free electron increases with the increase in the intensity of the incident light.
Contradiction : It is observed that the maximum kinetic energy acquired by photo electron ($\frac{1}{2}mv_{max}^2 = eV_0$) is same for both incident beams of different intensities $I_1$ and $I_2$ as shown in figure. This observation is contradictory to the fact explained with the help of the wave theory of light.
[(ii)] As per wave theory of light, electrons are emitted from the surface of the metal if it is exposed to a very intense beam of light. In other words, there is no role of the minimum or threshold frequency for the emission of electrons from the metallic surface.
Contradiction : It is also a contradiction to the observation that the frequency of the incident light should be greater than the threshold frequency to cause photoelectric emission.
[(iii)] As per wave theory of light , the energy of incident light is distributed over the wavefronts of incident light. When light falls on the surface of a metal, the energy absorbed per electron will be very small. Thus, each electron will take some time to have enough energy to overcome the surface barrier and hence to come out of the metallic surface. In other words, there should be enough time delay between the light falling on the metallic surface and the emission of electrons from the metallic surface.
Contradiction : It is observed that electrons are emitted from the metallic surface as soon as light is incident on it.
Thus, wave theory is unable to explain the photoelectric effect.