| − | A Photon is a quantised packet of electromagnetic radiation <ref>A French, P Taylor.(1978). A Introduction to Quantum Physics. MIT: CRC Press.</ref>. It is the elementary exchange particle for the electromagnetic force. The Energy of a photon (in Joules) depends on its frequency and is given by the equation: | + | A Photon is a quantised packet of electromagnetic radiation <ref>A French, P Taylor.(1978). A Introduction to Quantum Physics. MIT: CRC Press.</ref>. It is the elementary exchange particle for the electromagnetic force. The Energy of a photon depends on its frequency and is given by the equation: |