Quantum model of light?
When a clean plate is illuminated with low intensity ultraviolet light, photoelectons are emitted from its surface.
When the sodium plate is illuminated with red light, no photoelectrons are emmitted, even when the light intensity is very high
Explain these observations in terms of the quantum model of light?
Processing your request, Please wait....
The individual photons need to be of sufficient energy to kick out an electron. Otherwise the photons are just absorbed and re-emitted. It’s like shooting a thousand bullets at a tank instead of one big-ass rocket.
The quantum theory says that electromagnetic radiation(light) consist of localised bundle of quantized energy units called photon(similar to the concept of light particle).The expression for the amount of energy contained in a photon is directly proportional to its frequency, f, which is given by:
E=hf
h= planck’s constant
Hence the emission of photoelectrons from a photo emissive surface(which is measured as the current passing through the anode in a photoelectric cell) is dependent on the energy supplied to the electron in the form of electromagnetic radiation.This shows that by supplying electromagnetic radiation with high frequencies, an adequate amount of energy can be transfered to the electron to be emitted.In this case, UV light has higher frequency(hence higher energy) than the red light.
However, experimental results prove that the intensity of radiation(the amplitude of the wave) seem to have no effect on the photoemission of electron.