The Electromagnetic Spectrum (WJEC GCSE Science (Double Award)): Revision Note

The Electromagnetic Spectrum

• The electromagnetic spectrum (em) is a collection of waves that share the following properties:

  • They are all transverse

  • They can all travel through a vacuum

  • They all travel at the same speed in a vacuum

  • They all transfer energy

• There are 7 types of electromagnetic waves, which all together form a continuous spectrum

• The electromagnetic spectrum is arranged in a specific order based on the wavelengths or frequencies

The Electromagnetic Spectrum from Longest Wavelength to Shortest Wavelength

Visible light is just one small part of a much bigger spectrum: The electromagnetic spectrum

• The relationship between frequency and wavelength of waves across the electromagnetic spectrum is

  • The higher the frequency, the shorter the wavelength

  • The lower the frequency, the longer the wavelength

• This means that radio waves have a lower frequency, and a longer wavelength than UV waves

• This can be seen from the wave equation

• Where:

  •  = speed of the wave in metres per second (m/s)

  •  = frequency of the wave in hertz (Hz)

  •  = wavelength of the wave in metres (m)

• Since all electromagnetic waves travel at the speed of light in a vacuum, this is constant

  • Therefore, in the equation, in keeping v constant, if f increases then λ must decrease

Relationship Between Wavelength and Frequency

The larger the wavelength, the lower the frequency. The speed remains the same

• The higher the frequency, the higher the energy of the wave

• Waves with higher energy are:

  • Highly ionising

  • Harmful to cells and tissues causing cancer (e.g. UV, X-rays, Gamma rays)

  • For more information, see our revision note on Radiation

• Waves with lower energy are:

  • Useful for communications and they are used to transmit information, for example: 

    • Radio waves are used in long-range communications, such as for radio and television

    • Microwaves are used in mobile phones and satellite communications as they can penetrate the Earth's surface

    • Infra-red waves and visible light are used in optical fibres as they can undergo total internal reflection

  • Less harmful to humans