How do we know the energy of a photon (light particle) is quantised?

Firstly, quantisation of energy means that energy can only exist for specific, discrete values, i.e. it is not continuous. Now, photons display this phenomena however it is not immediately obvious why, as in classical physics, we observe that light acts as a wave. To understand how the we know these particles are quantised we have to investigate a some practical examples. One of these examples is called the photoelectric effect. This is where a electromagnetic radiation (light) is incident on a metal. This causes electrons to become excited and thus jump out of the metal under certain conditions. However as the intensity of the light increases the energy of the electrons does not, leading us to believe that the light is not behaving as a classical wave as first thought. Furthermore, we observe that no electrons are emitted if the frequency of the light is below a certain value, called the work function. These two observations lead us to draw the conclusion that light, in this experiment, is acting a particles of discrete energy.

Answered by Ben M. Physics tutor

2399 Views

See similar Physics A Level tutors

Related Physics A Level answers

All answers ▸

In an electric propulsion system, alpha particles are accelerated through a potential difference of 100kV at an average rate of 10^20 alpha particles per second. Calculate the average thrust the system can provide.


This Question is a multi-parter but all around the same scenario. Similar to an end of paper A-level physics question.


Use band theory to explain the changes in the resistance of an intrinsic semiconductor as temper changes.


One of the decays of potassium (A=40, Z=19) results in an excited argon atom with excess energy of 1.50 Mev. In order to be stable, it emits a gamma photon. What frequency and wavelength has this gamma photon?


We're here to help

contact us iconContact usWhatsapp logoMessage us on Whatsapptelephone icon+44 (0) 203 773 6020
Facebook logoInstagram logoLinkedIn logo

© MyTutorWeb Ltd 2013–2025

Terms & Conditions|Privacy Policy
Cookie Preferences