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What is Electromagnetic Radiation?

All electromagnetic radiation travels at the same speed (in a vacuum).
Electromagnetic radiation travels very quickly.
There is nothing which can travel faster.
The speed is 300,000,000 m/s in a vacuum
(that is 300 million metres per second - not easy to imagine!).

Electromagnetic radiation can be thought of as particles or waves
(the word radiation is also used for radioactivity).

Electromagnetic radiation has a wide variety of wavelengths
and frequencies which form the electromagnetic spectrum.

Electromagnetic waves are transverse waves
which have both an electric and a magnetic effect.
Electromagnetic waves are unusual because they
do not need any substance to get from one place to another.
They can travel through a vacuum.
Light and infra-red radiation (heat) can reach the Earth
from the Sun through the vacuum of space.

When is Electromagnetic Radiation a Particle and when is it a Wave?

It is not true that electromagnetic radiation
is sometimes a particle and sometimes a wave.
It always has the properties of being both a particle and a wave.
This site will mostly talk about electromagnetic radiation as waves
but you need to know a little about it being particles too.

What is a Photon?

When thought of as particles
electromagnetic radiation is often called a ray or a beam.
A ray or beam of electromagnetic radiation is made from particles
called photons. A photon is a packet of energy.
Different photons have different amounts of energy.

Three types of electromagnetic radiation
(ultraviolet, x-rays and gamma rays)
can form ions because the photons have enough energy
to remove an electron from an atom or molecule.
These three types are called ionising radiation
and they can all cause significant damage to living cells.

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