Uses of Electromagnetic Waves

The electromagnetic spectrum runs from radio waves (lowest frequency, longest wavelength) through microwave, infrared, visible light and ultraviolet, up to X-rays and gamma rays (highest frequency, shortest wavelength). Each group has practical uses that the specification asks you to recall.

EM group	Main uses to recall
Radio waves	Television and radio broadcasting
Microwaves	Satellite communications; cooking food
Infrared	Electric heaters; cooking food; infrared cameras
Visible light	Fibre-optic communications
Ultraviolet	Energy-efficient lamps; sun tanning
X-rays and gamma rays	Medical imaging and treatments

Learn this table in spectrum order. Examiners often give you one group and ask for a use, or give a use and ask which group is responsible.

The rest of this lesson takes each group in turn, states its use, and, for Higher Tier, explains why the properties of that wave make it suitable.

Radio waves are used for television and radio broadcasting. A transmitter sends out radio waves that carry the signal; an aerial on a television or radio picks them up.

(Higher Tier) Radio waves are suitable for broadcasting because they can travel long distances, and long-wavelength radio waves can diffract around hills and even follow the curve of the Earth, so they reach receivers that are not in a straight line from the transmitter.

Microwaves have two main uses. The first is satellite communications, such as satellite TV, phone signals and GPS.

(Higher Tier) Microwaves are suitable for satellite communication because they pass easily through the Earth's atmosphere, including cloud, so a signal can travel up to a satellite in orbit and back down to a receiver with little absorption.

The second use is cooking food in a microwave oven.

(Higher Tier) Microwaves used for cooking are absorbed by water molecules in the food, transferring energy that heats the food from the inside as well as the surface.

Infrared has three uses on the specification: electric heaters, cooking food and infrared cameras.

An electric heater, such as a grill or a toaster element, glows and emits infrared that is absorbed by nearby objects, transferring energy to them so they warm up. The same effect cooks food, for example under a grill.

(Higher Tier) Infrared is suitable for heating and cooking because it is readily absorbed by the surface of an object, transferring energy that raises the object's temperature.

An infrared camera (also called a thermal camera) detects the infrared radiation that all objects emit. Hotter objects emit more infrared, so the camera builds an image showing how the temperature varies across a scene.

(Higher Tier) Infrared cameras work because all objects emit infrared, and a hotter object emits more of it. Detecting the amount of infrared from each point lets the camera map temperature, which is useful for finding heat loss from buildings or people in the dark.

Infrared cameras are used for night vision, for spotting heat loss from houses, and in some medical checks.

Visible light is the narrow band of the spectrum that the human eye can detect. Its key use on the specification is fibre-optic communications.

An optical fibre is a thin strand of very pure glass. A signal is sent as pulses of light that travel down the fibre, reflecting off the inside walls again and again so the light stays trapped inside, even when the fibre bends.

(Higher Tier) Visible light (and infrared) is suitable for optical fibres because it can be reflected repeatedly along the fibre with very little energy lost, so data travels quickly over long distances and a huge amount of information can be carried at once.

This is why broadband internet, cable television and long-distance phone networks rely on optical fibres rather than copper wires: the signal loses far less energy and can carry far more data.

Ultraviolet (UV) has two uses: energy-efficient lamps and sun tanning.

An energy-efficient (fluorescent) lamp produces ultraviolet inside the tube, which strikes a coating that then glows with visible light. This produces light using less energy than an old filament bulb. In tanning, UV is absorbed by the skin, which responds by producing more of the pigment that darkens it.

(Higher Tier) UV is suitable for fluorescent lamps because it is emitted efficiently by the gas inside the tube and can be converted to visible light by a coating, giving bright light for little energy.

X-rays and gamma rays are used together in medicine for medical imaging and treatments.

(Higher Tier) X-rays are suitable for imaging bones because they pass through soft tissue but are absorbed by denser bone, so a shadow image reveals breaks. Gamma rays are used to treat cancer because they carry enough energy to kill cancer cells, and they can be directed at a tumour inside the body.

The same property that makes these rays hazardous, their high energy, is what makes them medically useful when carefully controlled.

1. Mixing up the uses of neighbouring groups

Microwaves cook and communicate with satellites; infrared heats and forms thermal images; radio broadcasts. Learning the uses in spectrum order stops you swapping microwave and infrared or radio and microwave.

2. Saying infrared and microwaves cook the same way

A microwave oven uses microwaves absorbed by water in the food; a grill or toaster uses infrared absorbed at the surface. Both cook, but by different waves. Name the correct group for the appliance in the question.

3. Saying optical fibres use X-rays or radio waves

Optical fibres carry visible light (and infrared). The whole point is that light reflects along the fibre with little loss. Do not name a wave the fibre cannot guide.

4. Not answering "why suitable" on Higher Tier questions

A Higher Tier "explain why this wave is used" question wants a property linked to the use, for example "microwaves pass through the atmosphere, so they reach a satellite". Simply naming the wave scores nothing on these questions.

5. Forgetting UV has two distinct uses

Ultraviolet is used both in energy-efficient lamps and in sun tanning. Students often recall only one. List both if the question asks for uses of UV.