Electromagnetic WavesEdexcel GCSE Physics: Revision notes
Section 1
What are the properties of electromagnetic waves?
All electromagnetic (EM) waves:
- Are transverse waves
- Travel at the same speed through a vacuum
- Transfer energy from a source to an observer
Our eyes can only detect a limited range of EM frequencies — the visible light part of the spectrum. Different substances can absorb, transmit, refract or reflect EM waves in ways that vary with wavelength (higher tier), and the velocities of EM waves differ in different substances (higher tier), which is why light refracts (bends) when it passes from one substance into another.
Sunlight travelling from the Sun (through the vacuum of space) to your eyes transfers energy — that's why sunlight warms your skin.
Section 2
What is the electromagnetic spectrum?
The EM spectrum is continuous, and is grouped into seven regions in order of increasing frequency (decreasing wavelength):
radio waves → microwaves → infrared → visible light (including all colours) → ultraviolet → x-rays → gamma rays
Radio waves have the longest wavelength and lowest frequency; gamma rays have the shortest wavelength and highest frequency.
Radio waves can be produced by, or can themselves induce, oscillations in electrical circuits (higher tier). Changes in atoms and nuclei can generate radiation across this wide frequency range, and can also be caused by the absorption of radiation.
Learn the order 'radio, micro, infra, visible, ultra, x-ray, gamma' — questions often ask you to place radiations in order of increasing frequency or decreasing wavelength.
Section 3
What are the dangers of electromagnetic radiation?
The potential danger of an EM wave increases with increasing frequency.
| Radiation | Harmful effect |
|---|---|
| Microwaves | internal heating of body cells |
| Infrared | skin burns |
| Ultraviolet | damage to surface cells and eyes, can lead to skin cancer |
| X-rays and gamma rays | mutation or damage to cells |
Higher-frequency radiations (UV, x-rays, gamma) carry more energy and can penetrate or ionise living tissue, which is why exposure must be limited and controlled.
Don't say 'radio waves are dangerous' — low-frequency radiations like radio waves and microwaves are generally far less hazardous than high-frequency ones like x-rays and gamma rays.
Section 4
What are electromagnetic waves used for?
- Radio waves: broadcasting, communications, satellite
- Microwaves: cooking, communications, satellite
- Infrared: cooking, thermal imaging, optical fibres, remote controls, security systems
- Visible light: vision, photography, illumination
- Ultraviolet: security marking, fluorescent lamps, detecting forged bank notes, disinfecting water
- X-rays: internal structure of objects, airport security, medical x-rays
- Gamma rays: sterilising food and medical equipment, detection and treatment of cancer
Must Know
- All EM waves are transverse, travel at the same speed in a vacuum, and transfer energy
- Spectrum order (increasing frequency): radio, microwave, infrared, visible, ultraviolet, x-ray, gamma
- Danger increases with increasing frequency
- Microwaves heat body cells; infrared causes skin burns; UV damages surface cells/eyes (skin cancer); x-rays and gamma rays cause mutation/cell damage
- Learn the key uses of each radiation type
- Substances absorb, transmit, refract or reflect EM waves differently depending on wavelength (higher tier)
That's the notes covered.
Carry on to the next subtopic.