The electromagnetic spectrum and its order, the properties of electromagnetic waves, the uses of each type of radiation, and the dangers of the higher-energy waves.

What this dot point is asking

Edexcel wants you to list the electromagnetic spectrum in order, describe the shared properties of electromagnetic waves, give the uses of each type of radiation, and explain the dangers of the higher-energy waves.

The electromagnetic spectrum

In order from longest wavelength (lowest frequency) to shortest wavelength (highest frequency):

1. Radio waves
2. Microwaves
3. Infrared
4. Visible light
5. Ultraviolet
6. X-rays
7. Gamma rays

Uses of each type

• Radio waves: broadcasting television and radio.
• Microwaves: cooking food, and satellite and mobile phone communication.
• Infrared: heaters and grills, thermal imaging, remote controls, and optical fibres.
• Visible light: seeing, photography, and fibre-optic communication.
• Ultraviolet: security marking (fluorescence), sun tanning, and sterilising water.
• X-rays: medical imaging of bones and airport security scanners.
• Gamma rays: sterilising medical equipment and food, and treating cancer.

Dangers

The higher-energy waves can harm the body:

• Ultraviolet damages skin cells, causing sunburn and increasing the risk of skin cancer, and can damage the eyes.
• X-rays and gamma rays are ionising: they can damage or change cells, causing mutations that may lead to cancer. Exposure is kept as low as possible, and workers use shielding.

The reason the higher-frequency waves are more dangerous is that they carry more energy. Radio waves and microwaves have low energy and mostly heat tissue at most, whereas ultraviolet, X-rays and gamma rays carry enough energy to remove electrons from atoms (to ionise them), which can damage DNA. This is the same reason these waves are useful in medicine: the energy that makes gamma rays dangerous also lets them kill cancer cells or sterilise equipment by destroying microorganisms.

Many uses depend on how each wave interacts with matter. Infrared is absorbed by surfaces and warms them, so it is used in heaters, grills and thermal cameras that detect the heat objects give off. Microwaves are absorbed by water molecules in food, heating it from within, and pass easily through the atmosphere, which is why they are used for satellite communication. Matching a wave to a use, and explaining it in terms of how the wave interacts with matter, is a common higher-mark question.

Try this

Q1. List the EM spectrum from longest to shortest wavelength. [2 marks]

• Cue. Radio, microwave, infrared, visible light, ultraviolet, X-rays, gamma rays.

Q2. Give one use of infrared radiation. [1 mark]

• Cue. Heating, thermal imaging, or remote controls (any one).