Question

Why photoelectric effect is not explained in terms of wave theory of light?

Answer 1

Photoelectric can be only explained by assuming that light is made up of particle not wave because

1. There is no time lag b/w incident of radiation and ejection of electrons. If light were a wave than electrons will take some time to come out from metal because light wave of same energy would be distributed over large number of electrons.
2. When we increase intensity of light(no.of photons falling per unit area) the no. of electrons emitted increase and the ratio is necessary to be like 1:1 according quantum mechanics. And if light were thought to be wave, on increasing its intensity or energy (only in wave) it's amplitude only gets change , so it will have no effect on number of electrons emitted rather it will have only change in kinetic energy of electron. Which shows that light is particle not wave because on increasing no. photon incidented no. of electrons emitted increases.
3. And when we increase frequency of radiation the more energy is supplied to electrons which increase their kinetic energy not number of electrons emitted.
4. According to wave physics energy of a wave depends upon amplitude of a wave it means that light of any frequency can make electrons come out from metal but it did not happens, light of certain fixed frequency can make electrons come out from metal. So, the photoelectric effect can only be explained by particle nature of light not wave.