Question

4) why doesn't the existence of a threshold frequency for the photoelectric effect make sense from the point of view of a continuous wave model of light?

4b) how does the concept of a photon explain the existence of a threshold frequency?

Answer 1

4. a) The photo electric effect is explained using the Quantum radiation theory of Max Plank, in which light is an electromagnetic radiation in which the energy is quantized.

Energy of each quanta is given by E = hv, where h is Plank's Constant and v : frequency of radiation. The wave theory fails miserably to predict the outcome, the theory just predicts that as the frequency of the wave increases it will increase the number of electrons emitted and as the amplitude increases, it should increase the kinetic Kinetic energy. Where it fails to explain the threshold frequency and photo electric effect.

According to wave theory, if the number of electrons emitted increases with the frequency of the wave there would have been at least one electron emitted with any frequency provided the intensity of the wave is quite high. But the theory is not at all true. That is according to wave physics energy of a wave depends upon amplitude of a wave.

According to quantum theory the velocity increases with increase in frequency above the threshold value. And number of electrons emitted depend on the intensity of the radiation.

4. b) In the case of photons the frequency corresponds to each quanta of radiation represents the energy of the photon. If the incoming photon is having enough energy to break the bond and make the material emit electron from the surface, it will contribute to the photo current. In quantum physics energy of the radiation depends on the frequency of the radiation.