Ans: Quantum electrodynamics or QED may be a quantum theory of the cooperations of electrically charged particles of the electromagnetic field. It is also called the relativistic quantum theory of electrodynamics. In essence, it describes how light and matter interact and is that the primary theory where full agreement between physics and therefore the special theory of relativity is achieved. QED mathematically describes all phenomena involving charged particles interacting using the exchange of photons and represents the quantum counterpart of classical electromagnetism giving a whole account of matter and light-weight interaction.