Question

How Classical theory fails to explain photo electric effect?

(Give complete explanation )

Answer 1

1. Within the limits of experimental accuracy (about 10^-9m) , there is no time interval between the arrival of light at a metal surface and the emission of photo electrons. However , because the energy in an em wave is supposed to be spread across the wave fronts, period of time should elapse before an individual electron accumulates enough energy to leave the metal, precise measurements infer that over a month would be needed for an atom to accumulate energy of the magnitude that photoelectrons from a sodium surface are observed to have .

2. A bright light yields more photoelectrons than a dim one of the same frequency, but the electron energies remain the same. The em theory of light, on the contrary, predicts that the more intense the light, the greater the energies of the electrons.

3. The higher the frequency of the light, the more energy the photoelectrons have . Blue light results in faster electrons than red light. At frequencies below a certain critical frequency , which is characteristic of each particular metal, no electrons are emitted. Above critical frequency the photoelectrons range in energy from 0 to maximum value that increases linearly with increasing frequency . This observation , also , cannot be explained by the em theory of light .