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Photon

Key Stage 5

Meaning

Photons (\(\gamma\)) are bosons responsible for mediating the electromagnetic interaction and are the particle associated with electromagnetic waves.

About Photons

The photon is denoted with the lower case Greek letter \(\gamma\) (gamma).
Photons carry energy from one place to another.
Photons have no mass or charge

About Virtual Photons

Virtual photons a model for the mechanism of action of the electromagnetic interaction, but they are not strictly 'real'.
Virtual photons have no mass and therefore can mediate the electromagnetic interaction over an infinite range.
Virtual photons carry momentum without carrying mass and are therefore able to change the direction of motion of other subatomic particles.
Virtual photons do not carry charge, but allow particles with charge to exchange momentum.

Equations

Momentum of a Photon

\(p = \frac{h}{\lambda}\)

Where

\(p =\) The momentum of the photon.

\(h = \) Planck's Constant (\(6.63\times10^{-34}Js\)).

\(\lambda =\) The wavelength of the wave associated with the photon.

Energy of a Photon

\(E = hf\)

Where

\(E =\) The energy of the photon.

\(h = \) Planck's Constant (\(6.63\times10^{-34}Js\)).

\(f =\) The frequency of the wave associated with the photon.

The Speed of Light

\(c = f\lambda\)

Where

\(c =\) The speed of light (\(3.00\times10^{8}ms^{-1}\) in a vacuum).

\(\lambda =\) The wavelength of the wave associated with the photon.

\(f =\) The frequency of the wave associated with the photon.

Examples

The virtual photon is shown mediating the electromagnetic interaction.
FeynmanDiagramProtonProton.png
FeynmanDiagramElectronElectron.png
This Feynman Diagram shows the electromagnetic interaction between two protons exchanging momentum via the virtual photon. This Feynman Diagram shows the electromagnetic interaction between two electrons exchanging momentum via the virtual photon.

References

AQA

Photons, page 95, GCSE Physics; Third Edition, Oxford University Press, AQA

OCR

Photons, pages 178-179, Gateway GCSE Physics, Oxford, OCR