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• There are seven types of electromagnetic (EM) waves, which make up the electromagnetic spectrum.
• Electromagnetic waves are transverse waves, and travel at the speed of light.
• Different types of electromagnetic wave have different uses and dangers.

There are lots of examples of electromagnetic waves around us, including light waves, radio waves and infrared radiation. These electromagnetic waves are caused by vibrating electric and magnetic fields and they are transverse waves, because the vibrations of these fields are at right angles to the direction the wave travels.

Electromagnetic waves travel at an extremely high speed: the speed of light. The speed of light in a vacuum is around 300,000,000 metres per second. At that speed, light can travel 7.5 times around Earth in just one second.

There are seven distinct groups of electromagnetic waves which make up the electromagnetic spectrum.

A mnemonic is often used to help remember the electromagnetic waves in the correct order.

This is a sentence that can remind you of the first letter of each type of wave, in order of increasing frequency – for example:

Electromagnetic waves have a wide range of uses. The specific uses depend on the type of electromagnetic wave.

Radio waves

Radio waves are used for sending radio and television signals. They are also used to control radio-controlled toys, like cars, boats and aeroplanes. We even use radio waves in astronomy, to find out about distant stars and galaxies by studying the radio waves they produce.

Microwaves

As well as heating food in microwave ovens, microwaves are used for communication. For example, mobile phones, and wireless internet (Wi-Fi) devices like laptop computers all use microwaves to communicate. Microwaves are also used for sending satellite signals, eg for GPS systems or satellite television.

Infrared

Infrared (IR) waves are emitted by all warm objects, and they are used for heating and to cook food in ovens, grills and toasters. They are also used for communication, including remote controls for televisions and stereos, as well as sending internet and telephone signals along optical fibres. Infrared waves can also be detected by infrared cameras, so are often used by night vision cameras or thermal imaging cameras in police helicopters – which can detect the infrared waves emitted by people and animals.

Visible light

This is the only type of electromagnetic radiation which is visible to the human eye. As well as allowing people to see the world around them, visible light has a range of other uses, including forming images in cameras and video cameras. Concentrated visible light emitted by lasers can be used to send internet and telephone signals along optical fibres. Lasers can even be used in surgery, and to cut materials like wood and metals in a laser cutter.

Ultraviolet

Ultraviolet (UV) waves are used in forensic science to help detect forged documents, like fake banknotes, passports or driving licences. Ultraviolet waves can be absorbed by some materials, like fluorescent inks in highlighter pens, making them glow brightly. They are also used to disinfect water, by killing bacteria.

X-rays

X-rays are commonly used to produce medical images of broken bones, because they can pass through body tissues but are absorbed by bones. They are used to sterilise medical equipment, killing any bacteria present before the instruments are used for surgery. X-rays are also used in airport security scanners and to detect broken pipes underground.

Gamma rays

Gamma rays are also used to produce medical images and to sterilise medical instruments, in a similar way to X-rays. They are also used to sterilise food, killing bacteria in fresh fruit and vegetables to increase their shelf life. Gamma rays can also be used to detect and even to treat cancer.

Although electromagnetic waves have many uses, they can also be dangerous. Different types of EM wave can be dangerous in different ways.

Microwaves

Because microwaves have a heating effect, some powerful microwaves can be dangerous. Your microwave oven will not switch on if the door is open, to prevent the microwaves causing damage to the cells in your body by heating them.

Infrared

The heating effect of infrared waves can cause burns to your skin.

Visible light

Concentrated visible light (eg from a laser or the Sun) can cause eye damage or even blindness.

Ultraviolet

Ultraviolet (UV) radiation can cause eye damage, which is why most sunglasses can absorb UV, preventing it from reaching the eye. The intense UV emitted by the Sun is absorbed by your skin and can cause sunburn or even damage DNA in your body cells – which could lead to skin cancer.

X-rays

X-rays can also damage DNA in body cells, which could lead to cancers developing inside the body. For low levels of exposure (eg a few medical x-rays per year) this is not a significant problem, but radiographers and other people working with X-rays must take precautions to reduce this risk.

Gamma rays

Like X-rays, gamma rays can also damage DNA in your body cells which can lead to cancers developing inside the body. People working with radioactive substances which emit gamma rays must limit the amount of gamma radiation they are exposed to, by wearing protective clothing and restricting the time they work near these materials.

Each region of the electromagnetic spectrum has a range of wavelengths associated with it. The range of wavelengths affects the way each type of EM wave behaves and interacts with matter.