The energy delivered by a beam of electromagnetic radiation at any place depends on:
- the number of photons arriving there and
- the energy each photon delivers.
Consider two microwave ovens. Both produce microwave radiation whose photons each carry the same amount of energy. But the more powerful microwave oven will deliver more photons each second.
The intensity of electromagnetic radiation is the rate at which energy arrives at a surface, i.e. how much energy arrives each second. The intensity can be increased by:
- increasing the number of photons arriving each second, and/or
- increasing the energy of each photon.
So, for the same number of photons per second, gamma radiation will produce a higher intensity beam than radio waves, because gamma ray photoms have a much greater energy than radio wave ones do.
The
effect of distance
The intensity of a beam of electromagnetic radiation decreases with distance from its source. This is because the energy is spread over a larger surface area.