Electromagnetic Waves and Their Properties

This section explains electromagnetic waves and their properties covering, the electromagnetic spectrum, the visible spectrum, refraction and radio waves.

Electromagnetic Waves

Electromagnetic (EM) waves are transverse waves that transfer energy from one place to another without requiring a medium. They consist of oscillating electric and magnetic fields that travel at right angles to each other and to the direction of wave propagation. EM waves all travel at the same speed in a vacuum: 3.0 × 10⁸ m/s (the speed of light).

The Electromagnetic Spectrum

The EM spectrum consists of a range of waves with different wavelengths and frequencies, arranged in order of decreasing wavelength and increasing frequency:

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1. Radio Waves – Longest wavelength, lowest frequency
2. Microwaves
3. Infrared Radiation
4. Visible Light
5. Ultraviolet Radiation
6. X-rays
7. Gamma Rays – Shortest wavelength, highest frequency

Each type of wave has unique properties and uses, such as communication, medical imaging, and sterilisation.

The Visible Spectrum

The visible part of the EM spectrum is the light that human eyes can detect. It ranges from red (longest wavelength) to violet (shortest wavelength). The sequence of colours in the visible spectrum is remembered using the acronym ROYGBIV (Red, Orange, Yellow, Green, Blue, Indigo, Violet). Different wavelengths of visible light correspond to different colours.

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Refraction

Refraction is the bending of a wave when it passes from one medium to another due to a change in speed. When light moves from air into glass or water, it slows down and bends towards the normal. When it moves from glass or water into air, it speeds up and bends away from the normal. This is why objects under water appear distorted. The refractive index of a material determines how much light is refracted.

Radio Waves

Radio waves have the longest wavelengths and lowest frequencies in the EM spectrum. They are used for communication, including radio and television broadcasting, mobile phones, and satellite transmissions.

• Long-wave radio (1–10 km wavelength) can diffract around hills and buildings.
• Short-wave radio (10–100 m wavelength) can reflect off the ionosphere, allowing long-distance transmission.

Radio waves are produced by oscillations in electrical circuits and can be detected by aerials, where they induce alternating currents that carry information.

This guide summarises the key properties and behaviours of electromagnetic waves, an essential topic in GCSE Physics.