The Photon (Cambridge (CIE) A Level Physics): Revision Note

In classical wave theory, electromagnetic (EM) radiation is assumed to behave as a wave

This is demonstrated by the fact EM radiation exhibits phenomena such as diffraction and interference

However, experiments from the last century, such as the photoelectric effect and atomic line spectra, can only be explained if EM radiation is assumed to behave as particles

These experiments have formed the basis of quantum theory, which will be explored in detail in this section

Photons are fundamental particles which make up all forms of electromagnetic radiation

A photon is a massless “packet” or a “quantum” of electromagnetic energy

• They are sometimes referred to as 'particles of light'

What this means is that the energy is not transferred continuously but as discrete packets of energy

In other words, each photon carries a specific amount of energy and transfers this energy all in one go, rather than supplying a consistent amount of energy