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Electromagnetic spectrum

The electromagnetic spectrum is a continuous range of related waves. The waves in this spectrum are called electromagnetic waves or electromagnetic radiation.

Different types of electromagnetic waves are characterised by their frequencies and wavelengths. Waves which have a higher frequency have more energy.

All of the waves in the spectrum share the following properties:

  • They are transverse waves.
  • They can travel through a vacuum
  • They travel at the same speed in a vacuum $$ (3 \times 10^{8} \text{ m/s})$$.
  • They transmit energy.

Different types of electromagnetic waves are used for different purposes depending on their frequencies.

Electromagnetic wave Frequency (Hz) Uses
Radio waves Lowest Communications, radios, televisions
Microwaves Mobile communications, cooking food
Infrared (IR) Remote controls, night vision cameras
Light Seeing, lasers, photography
Ultraviolet (UV) Tanning beds, Security markings on bank notes and ID cards
X-rays Checking for broken bones, airport security
Gamma rays Highest Sterilising equipment, killing cancerous cells in radiotherapy
Light is a type of electromagnetic wave. It is used in lasers.
Light is a type of electromagnetic wave. It is used in lasers.

An electromagnetic wave is absorbed when the energy of the wave is transferred to an object.

Plants absorb visible light from the sun which they use to make chemical energy.

The effect of absorbing electromagnetic waves depends on the energy of the radiation and the amount of exposure.

Higher energy radiation is more dangerous than lower energy radiation. The danger from absorbing electromagnetic radiation is increased with greater exposure.

Absorption of all types of radiation causes heating:

  • Microwaves are used to heat up food.
  • Ultraviolet rays from the sun can cause skin to turn red and burn.
A severe case of sunburn.
A severe case of sunburn.

Ionisation is the process of forming an ion by the addition or removal of charged particles such as electrons.

A hydrogen atom is ionised when an electron is removed.

Ionising radiation is any type of radiation that has enough energy to cause ionisation when it is absorbed by an object.

High energy electromagnetic radiation such as X-rays and gamma rays is ionising radiation.

Ionising radiation causes damage to living tissue by changing the molecules in them. This can destroy living cells in the body and increases the risk of developing cancer.

Ionising radiation hazard symbol.
Ionising radiation hazard symbol.