Virtual photon
A virtual photon is an ephemeral force-carrying particle (exchange particle) that transmits the electromagnetic force between charged particles. Virtual photons exist for an extremely brief time allowed by the uncertainty principle and mediate interactions like Coulomb repulsion between electrons.
Real World
When two electrons in a copper wire repel each other and maintain spacing, that repulsion is mediated by virtual photons exchanged billions of times per second — the quantum mechanism behind everyday electrical resistance.
Exam Focus
On Feynman diagrams, draw virtual photons as wavy lines between charged particles and label them clearly to gain the communication mark.
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