CIE A Level Physics (9702) 2019-2021

Revision Notes

8.5.1 Electromagnetic Spectrum

From Radio Waves to Gamma Rays

  • The electromagnetic spectrum is arranged in a specific order based on their wavelengths or frequencies
  • This order is shown in the diagram below from longest wavelength (lowest frequency) to shortest wavelength (highest frequency)


EM spectrum diagram, downloadable AS & A Level Physics revision notes

Energy, wavelength and frequency for each part of the electromagnetic spectrum


  • The higher the frequency, the higher the energy of the radiation
  • Radiation with higher energy is highly ionising and is harmful to cells and tissues causing cancer (e.g. UV, X-rays, Gamma rays)
  • The approximate wavelengths in a vacuum of each radiation is listed in the table below:


EM spectrum wavelengths and frequencies

Table of EM spectrum wavelengths and frequencies, downloadable AS & A Level Physics revision notes

  • To alternatively find the range of frequencies, convert the wavelengths using the wave equation: c = fλ where c is the speed of light: 3.0 × 108 m s-1


Worked Example

A is a source emitting microwaves and B is a source emitting X-rays.

The table suggests the frequencies for A and B. Which row is correct?

Worked example - wavelength and frequency (2), downloadable AS & A Level Physics revision notes

Exam Tip

You will be expected to memorise the range of wavelengths for each type of radiation, however you don’t need to learn the frequency ranges by heart. Since all EM waves travel at the speed of light, you can convert between frequency and wavelength using the wave equation in an exam question.

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