The intensity of ❌ radiation gets less as you move ❌ away from the source. The intensity of the Sun's radiation decreases further away from it because it is spread over a ❌ area. This is why planets more distant from the Sun than the Earth are much ❌ than our planet. The earth receives more of the Sun's electromagnetic radiation because the intensity of the radiation is ❌ closer to the Sun.
❌ = energy transferred per second per m^2.
If you move a torch closer to a surface, its light spreads over a smaller area and becomes ❌. The total energy from the torch each second is the ❌, but the intensity of light on the surface increases. This happens because as the distance ❌, the area the energy spreads over increases four-fold, and so the intensity ❌ four-fold.

Radiation workers increase their risk of exposure to X-rays and ❌ rays. They can choose whether to accept this ❌. The risk can be monitored using ❌, allowing problems to be spotted before too much harm is done.
People who have mobile phone ❌ built near their homes have exposure to ❌ forced upon them. They tend to be less ❌ to accept any level of risk, and are more likely to ❌ possible risks.

Ozone is produced when oxygen ❌ absorb high energy UV radiation and react together. Ozone molecules may split into an oxygen molecule and a free oxygen ❌ if they absorb low energy UV radiation. In both these reactions, ❌ radiation is emitted. Ozone also reacts with nitrogen, hydrogen, chlorine and bromine ❌.
The absorption of ❌ radiation in the ozone layer reduces the amount of ultraviolet radiation reaching the Earth's ❌. It also causes ❌ changes in this part of the atmosphere.

There are several advantages of sending information using ❌ signals:
- different types of ❌ can be sent at the same time
- digital signals can be sent more accurately than ❌ signals
- digital information can be stored and ❌ by computers.
- digital signals can only take certain ❌, so it is easy to tell which part of the signal is real and what is ❌ (unwanted information mixed in with the original signal).