The Electromagnetic Spectrum (OCR A Level Physics)

• Visible light is just one part of a much bigger spectrum: The Electromagnetic Spectrum
• All electromagnetic waves have the following properties in common:
  • They are all transverse waves
  • They can all travel in a vacuum
  • They all travel at the same speed in a vacuum (free space) — the speed of light

• The speed of light in air is approximately the same as in a vacuum

Oscillating electric and magnetic fields in an electromagnetic wave

• These transverse waves consist of electric and magnetic fields oscillating at right angles to each other and to the direction in which the wave is travelling (in 3D space)
• Since they are transverse, all waves in this spectrum can:
  • Reflect
  • Refract
  • Diffract
  • Be polarised
  • Produce interference patterns

The Electromagnetic Spectrum

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

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)

Uses of EM Waves

• Electromagnetic waves have a large number of uses
• The main uses are summarised in the table below:

• The approximate wavelengths in a vacuum of each radiation are listed in the table below:

Table of EM spectrum wavelengths and frequencies

• 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