- Electromagnetic radiation is also called EM radiation, EMR and electromagnetic radiant energy.
- Stars including the sun radiate electromagnetic energy through space at every wavelength of the electromagnetic spectrum.
- When the waveform of electromagnetic radiation is being considered, electromagnetic energy is measured by calculating the frequency of the electromagnetic waves.
- The unit used to calculate frequency is the hertz (Hz). One hertz equals one wave-cycle per second.
- When electromagnetic radiation is being considered in terms of photons, the elementary particles of the electromagnetic field, then the higher the photon’s frequency, the higher its energy and the longer the photon’s wavelength, the lower its energy.
- Photon energy is solely a function of the photon’s wavelength and frequency.
- Other factors, such as the intensity of the radiation, do not affect photon energy. In other words, two photons of light with the same colour and therefore, same frequency, will have the same photon energy, even if one was emitted from a wax candle and the other from the Sun.
- Units of energy commonly used to denote photon energy are the electronvolt (eV) and the joule. Whilst power is measured in joules per second.