Uses and applications of electromagnetic waves — AQA GCSE Combined Science

Radio waves are electromagnetic waves with the longest wavelengths and lowest frequencies in the spectrum. They travel at the speed of light in a vacuum. They are used for television and radio broadcasting. (HT only) Students must explain why radio waves are suitable for these applications and how they are produced. In television and radio, an alternating current in a transmitting aerial generates radio waves. These waves travel to a receiver, where they induce an alternating current of the same frequency, which is then decoded into sound and pictures. Longer radio wavelengths can diffract (bend) around obstacles like hills, while shorter ones require a direct line of sight.

Microwaves are electromagnetic waves with shorter wavelengths and higher frequencies than radio waves. They are used for satellite communications and cooking food. (HT only) Students must explain why microwaves are suitable for these applications. Microwaves can pass easily through the Earth's atmosphere and are not strongly absorbed by it, so they are used to send signals to and from satellites. In a microwave oven, microwaves penetrate the outer layers of food and are absorbed by water molecules, causing them to vibrate and gain kinetic energy. This raises the temperature of the water, and the heat is then transferred to the rest of the food by conduction.

Infrared is electromagnetic radiation with wavelengths just longer than red visible light. All warm objects emit it, and its intensity rises with temperature. Electrical heaters contain a heating element that becomes hot; the element emits infrared, which travels to nearby objects and surfaces and is absorbed, increasing their internal energy and warming them. Cooking food works the same way: a grill element radiates infrared that is absorbed by the food surface, heating and browning it, while a microwave oven instead uses microwaves. Infrared cameras detect the infrared emitted by objects and build a thermal image, so warmer regions appear brighter. They are used in night vision, thermal imaging of buildings to find heat loss, and medical screening. Infrared can be reflected, absorbed or transmitted, and its heating effect depends on the surface absorbing it.

Visible light is the narrow band of the electromagnetic spectrum detected by the human eye. In fibre optic communication, light carrying a signal travels along a thin glass or plastic fibre. The light rays bounce back and forth off the inside walls of the fibre, reflecting completely so that the light stays inside the core, even around bends. Pulses of light encode digital information, allowing signals to travel long distances with little loss for telephone and internet networks. (HT only) Students must explain the suitability of visible light for this application: it has a shorter wavelength and higher frequency than infrared or microwaves, enabling it to carry more information per second.

Ultraviolet (UV) lies just beyond the violet end of the visible spectrum, with wavelengths roughly 10⁻⁸ m to 4 × 10⁻⁷ m and frequencies above those of visible light. Its higher frequency means each photon carries more energy than visible photons, so UV can excite certain materials and cause chemical change. This explains two contrasting uses. In an energy-efficient lamp, a mercury vapour discharge emits UV, which is absorbed by a phosphor coating that re-emits visible light, giving more useful light per joule than a filament lamp. In sun tanning, UV is absorbed by skin, stimulating melanin production and darkening the skin; overexposure damages DNA and causes sunburn, ageing and increased skin cancer risk. Students should link use to property: high photon energy for fluorescence, and biological absorption for tanning, while recognising the hazard and the need to limit exposure.

X-rays and gamma rays are ionising electromagnetic radiation with very short wavelengths and very high frequencies, so their photons carry enough energy to remove electrons from atoms. This property makes them useful in medicine but also hazardous. In imaging, X-rays pass through soft tissue more easily than through bone or metal, so a detector behind the patient records a shadow image; gamma cameras detect gamma rays emitted by a tracer inside the body, giving functional images. In treatment, carefully directed X-rays or gamma rays can kill cancer cells by damaging their DNA, often using multiple beams so the tumour receives a high dose while surrounding tissue receives less. Students should connect each use to penetration and ionisation, and explain how dose, shielding and targeting control the risk.

Higher Tier students must link a wave property to each named use. Radio waves travel long distances for television and radio. Microwaves pass through the atmosphere for satellite links and are absorbed by water in food. Infrared is emitted and absorbed by warm objects, so it suits heaters, cooking and thermal cameras. Visible light can carry signals through optical fibres by internal reflection. Ultraviolet causes fluorescence in energy-efficient lamps and affects skin pigment in sun tanning. X-rays pass through soft tissue more than bone for imaging, while penetrating gamma rays can treat tumours. Each answer should state both the useful property and the application.