Question

Why photoelectric effect cannot be explained by classical physics?

Answer 1

Solution:

The Photo-electric effect can not be explained by classical physics because of the following factors:

1. Absence of lag time: When electromagnetic radiation is incident on a metal surface with a frequency more than the threshold frequency, then electrons are emitted immediately from the metal surface even for low-intensity radiation. This absence of lag time contradicts classical physics understanding, in which irradiated electrons would take a significant time to gain energy before they can leave the metal surface.
2. Dependence of kinetic energy of photoelectron on the intensity of the incident radiation: In the photoelectric effect, the kinetic energy of photoelectrons is independent of the intensity of incident radiation and depend on the frequency of the incident radiation.
3. Threshold frequency: Every metal surface has a threshold frequency, any electromagnetic radiation having a frequency below this threshold frequency cannot eject an electron. But according to classical physics, any incident radiation will eject the electron if given sufficient time for the electron to gain the energy.

Thus, due to the above factors, the Photo-electric effect can not be explained by classical physics.