What you'll learn
This guide covers the practical applications and potential dangers of all seven types of electromagnetic radiation. You'll learn how each part of the electromagnetic spectrum is used in everyday technology and medicine, understand why different wavelengths have different effects on living tissue, and be able to explain safety precautions. This content is frequently tested in AQA GCSE Physics Paper 2.
Key terms and definitions
Electromagnetic spectrum — the complete range of electromagnetic waves ordered by wavelength or frequency, from radio waves (longest wavelength) to gamma rays (shortest wavelength)
Ionising radiation — electromagnetic waves with sufficient energy to remove electrons from atoms, creating ions; includes ultraviolet (shorter wavelengths), X-rays and gamma rays
Mutation — a change in the DNA of a cell caused by ionising radiation, which may lead to cancer
Microwave — electromagnetic waves with wavelengths between approximately 1 mm and 30 cm, used for satellite communications and cooking
Ultraviolet (UV) radiation — electromagnetic waves with wavelengths shorter than visible light but longer than X-rays, emitted by the Sun and some artificial sources
Fibre optic cable — a thin strand of glass or plastic that transmits data as pulses of visible light or infrared radiation through total internal reflection
Carrier wave — a radio wave or microwave used to transmit information by varying its amplitude or frequency
Absorbed dose — the amount of energy from radiation absorbed per kilogram of tissue, measured in grays (Gy)
Core concepts
Radio waves
Uses:
Broadcasting: Radio waves with wavelengths of 1 m to 10,000 m transmit television and radio programmes. Long wavelengths diffract around hills and buildings, enabling widespread coverage.
Communications: Short-wave radio bounces off the ionosphere, allowing transmission over large distances across the Earth's surface without satellites.
Bluetooth and WiFi: Very short radio waves (approximately 10 cm) transmit data between devices over short distances.
Hazards:
Radio waves are non-ionising and generally considered safe at normal exposure levels. They do not have enough energy to damage living cells or cause mutations. Some studies investigate whether prolonged exposure to radio frequency radiation from mobile phone masts affects health, but current evidence shows no confirmed harmful effects at regulated power levels.
Microwaves
Uses:
Satellite communications: Microwaves pass easily through the Earth's atmosphere with minimal absorption. Satellites receive signals from ground stations, amplify them, and retransmit to other locations. The microwave signal must be directed precisely at the satellite using a curved transmitter dish.
Mobile phone networks: Phone masts transmit and receive microwave signals. The short wavelength requires direct line-of-sight between masts and devices.
Cooking: Microwave ovens use microwaves with a frequency of approximately 2,450 MHz. Water molecules in food absorb this radiation, causing them to vibrate and heat up through friction. The microwaves penetrate several centimetres into food.
Hazards:
Microwaves heat water molecules in living tissue. Internal heating of body tissue can occur if exposure is intense enough, potentially causing burns beneath the skin surface. Microwave ovens have metal shielding and safety cut-off switches to prevent exposure. There is ongoing research into whether long-term, low-level microwave exposure from mobile phones affects brain tissue, though current evidence suggests risks are minimal at regulated levels.
Infrared radiation
Uses:
Thermal imaging: All objects emit infrared radiation; hotter objects emit more. Infrared cameras detect this radiation to create images showing temperature differences, used in search and rescue operations, security systems, and detecting heat loss from buildings.
Infrared heaters: Electric heaters and toasters emit infrared radiation that is absorbed by objects and people, transferring energy and causing heating.
Optical fibre communications: Infrared radiation travels through fibre optic cables carrying telephone and internet data. Infrared has a higher frequency than radio waves, allowing more information to be transmitted.
Remote controls: Television and other device remote controls emit pulses of infrared radiation to send signals.
Infrared scanners: Used in security systems to detect intruders through body heat.
Hazards:
Infrared radiation causes heating. Prolonged or intense exposure can cause skin burns. Infrared radiation can also damage the eyes, particularly the retina if the source is very intense (such as looking at arc welding). Protective equipment should be worn when working with intense infrared sources.
Visible light
Uses:
Vision: The human eye detects visible light, enabling us to see. Different wavelengths are perceived as different colours.
Photography: Cameras record images using visible light focused onto sensors or photographic film.
Fibre optic communications: Like infrared, visible light pulses travel through optical fibres to transmit data at high speeds with minimal energy loss.
Illumination: Light bulbs, LEDs, and other sources provide lighting for homes, streets, and workplaces.
Hazards:
Very bright visible light can damage the retina of the eye, potentially causing temporary or permanent blindness. Never look directly at the Sun or intense light sources such as lasers. Lasers produce intense, parallel beams of visible light (or sometimes infrared or UV) that can cause severe eye damage. Safety goggles must be worn when working with powerful lasers.
Ultraviolet radiation
Uses:
Fluorescent lamps: UV radiation inside the tube causes a phosphor coating to fluoresce, emitting visible light. Energy-efficient bulbs and strip lights use this principle.
Security marking: Banknotes and passports contain ink that fluoresces under UV light, helping to detect forgeries.
Disinfection: UV radiation kills bacteria and viruses by damaging their DNA. Used in water treatment plants, hospitals, and air purification systems.
Sun tanning: Controlled UV exposure in tanning beds stimulates melanin production in skin, though this practice carries significant health risks.
Hazards:
UV radiation is ionising (particularly UV-B and UV-C with shorter wavelengths). It can:
Cause sunburn: UV-B radiation damages skin cells, causing inflammation, pain, and peeling.
Increase skin cancer risk: UV radiation causes mutations in skin cell DNA. Repeated exposure, particularly sunburn, significantly increases the risk of melanoma and other skin cancers.
Cause premature skin aging: Breakdown of collagen fibres leads to wrinkles and age spots.
Damage eyes: Can cause photokeratitis ("snow blindness") and increase cataract risk.
Protection: Use sunscreen with appropriate SPF, wear protective clothing and sunglasses, avoid midday sun, and never use tanning beds.
X-rays
Uses:
Medical imaging: X-rays pass through soft tissue but are absorbed by bones and metal. Detectors on the opposite side of the body create shadow images showing bone fractures, dental cavities, and foreign objects. Contrast media (barium meals, iodine injections) make soft tissues visible.
CT (computed tomography) scans: Multiple X-ray images taken from different angles are combined by computer to create detailed 3D images of internal organs.
Airport security: Baggage scanners use X-rays to inspect luggage contents without opening bags.
Cancer treatment (radiotherapy): High-dose, focused X-rays kill cancer cells. Beams are directed from multiple angles so healthy tissue receives minimal exposure while the tumour receives a concentrated dose.
Hazards:
X-rays are highly ionising. They can:
Cause mutations: Damage to DNA may lead to cancer. Risk increases with cumulative exposure.
Kill cells: High doses destroy tissue, causing radiation burns.
Harm developing foetuses: Pregnant women avoid X-rays unless absolutely necessary because rapidly dividing cells are particularly vulnerable.
Protection: Lead aprons shield parts of the body not being imaged. Radiographers leave the room or stand behind lead screens. Exposure time and radiation dose are minimised. The benefit of medical diagnosis must outweigh the small cancer risk.
Gamma rays
Uses:
Sterilisation: Gamma rays kill bacteria, viruses, and fungi on medical instruments, food, and surgical equipment. The items can be sealed in packaging before irradiation, maintaining sterility.
Cancer treatment (radiotherapy): Gamma radiation from radioactive sources (such as cobalt-60) is directed at tumours. Multiple beams from different angles concentrate the dose on the cancer while limiting damage to surrounding healthy tissue.
Medical tracers: Radioactive substances that emit gamma rays are injected or swallowed. Gamma cameras detect the radiation to show how organs function or locate tumours. Technetium-99m is commonly used because it has a short half-life (6 hours) and emits gamma rays but not heavily ionising alpha or beta particles.
Sterilisation of food: Irradiating food with gamma rays extends shelf life by killing microorganisms without significantly affecting taste or nutritional value. The food does not become radioactive.
Hazards:
Gamma rays are the most penetrating and ionising electromagnetic radiation. They:
Cause severe cell damage: Can destroy cells throughout the body, leading to radiation sickness at high doses.
Increase cancer risk significantly: Even small doses increase mutation risk. Effects are cumulative over lifetime exposure.
Cause radiation burns: High doses kill skin cells and underlying tissue.
Protection: Thick lead or concrete shielding blocks gamma rays. Radioactive sources are stored in lead-lined containers. Workers monitor their exposure using radiation badges. Time, distance, and shielding are the three key safety principles. Medical use is carefully justified, and doses are minimised.
Worked examples
Example 1: Explain why microwaves are used for satellite communication rather than radio waves. [3 marks]
Answer:
- Microwaves can pass through the Earth's atmosphere without significant absorption [1 mark]
- Radio waves (with longer wavelengths) would be absorbed or reflected by the ionosphere [1 mark]
- Microwaves can carry more information due to their higher frequency [1 mark]
Example 2: A hospital uses X-rays for medical imaging. Describe two safety precautions that should be taken and explain why each is necessary. [4 marks]
Answer:
- Lead aprons are worn by patients to shield parts of the body not being imaged / because X-rays are ionising and can cause mutations in DNA / leading to cancer [2 marks]
- Radiographers stand behind a lead screen or leave the room / because repeated exposure increases their cumulative radiation dose / increasing long-term cancer risk [2 marks]
Example 3: A student suggests using gamma rays instead of visible light for fibre optic communication. Evaluate this suggestion. [3 marks]
Answer:
- Gamma rays would transmit data at similar speeds to visible light / both are electromagnetic waves travelling at 3 × 10⁸ m/s in a vacuum [1 mark]
- However, gamma rays are ionising and dangerous to health / would pose serious safety risks during installation and maintenance [1 mark]
- Visible light and infrared are safe, effective, and cheaper for this purpose [1 mark]
Common mistakes and how to avoid them
Confusing ionising and non-ionising radiation: Remember that only UV (shorter wavelengths), X-rays, and gamma rays are ionising. Radio waves, microwaves, infrared, and visible light are non-ionising. Ionising radiation has enough energy to remove electrons from atoms.
Stating that microwaves "cook from the inside out": Microwaves penetrate only a few centimetres into food. The outside heats first, then energy conducts inward. Don't claim microwaves heat the centre first.
Claiming all UV radiation causes cancer immediately: UV increases cancer risk through cumulative DNA damage over time. A single exposure rarely causes cancer, but repeated exposure (especially sunburn) significantly increases risk.
Forgetting that hazard depends on dose and exposure time: Low doses of X-rays for medical diagnosis carry minimal risk compared to the diagnostic benefit. High doses over long periods are dangerous. Always consider the balance of risk versus benefit.
Mixing up uses across different wave types: Be specific. For example, satellite communication uses microwaves, not radio waves. Thermal imaging uses infrared, not microwaves. Learn the specific uses for each type.
Stating that irradiated food becomes radioactive: Food exposed to gamma rays does not become radioactive. The radiation kills microorganisms but does not make the food emit radiation itself.
Exam technique for "Uses and hazards of electromagnetic waves"
"Describe" questions require you to state features or characteristics. For safety precautions, state what is done and why. Aim for one mark per distinct point.
"Explain" questions need reasons or mechanisms. For hazards, link the radiation type to its effect on cells (heating or ionisation) and the resulting harm. Use because/therefore to structure answers.
Extended response (6-mark) questions might ask you to compare uses and hazards across multiple wave types. Plan your answer: write about one wave type, then another, covering both uses and hazards for each. Use scientific terminology precisely.
Command word "evaluate" means weigh up advantages and disadvantages, then reach a judgment. Consider both benefits (medical diagnosis, communication) and risks (cancer, burns) before concluding.
Quick revision summary
The electromagnetic spectrum ranges from radio waves to gamma rays. Radio waves and microwaves enable communication and broadcasting. Infrared provides heating and thermal imaging. Visible light allows vision and photography. UV sterilises and causes fluorescence but damages skin and increases cancer risk. X-rays and gamma rays provide medical imaging and cancer treatment but are highly ionising, requiring strict safety precautions including shielding, minimising exposure time, and justifying medical use.