Electromagnetic Waves (Cambridge (CIE) O Level Physics) : Revision Note

Electromagnetic Waves

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

• The main groupings of the continuous electromagnetic (EM) spectrum in order of increasing frequency and decreasing wavelength are:

  • Radio waves

  • Microwaves

  • Infrared

  • Visible (red, orange, yellow, green, blue, indigo, violet)

  • Ultraviolet

  • X-rays

  • Gamma rays

• This order is shown in the diagram below from longest wavelength (lowest frequency) to shortest wavelength (highest frequency)

The Spectrum of Electromagnetic Waves

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

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

• Radiation with higher energy is:

  • Highly ionising

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

• Radiation with lower energy is:

  • Useful for communications

  • Less harmful to humans

Properties of Electromagnetic Waves

• Electromagnetic waves are defined as:

  Transverse waves that transfer energy from the source of the waves to an absorber

• All electromagnetic waves 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

• The 7 types of electromagnetic waves together form a continuous spectrum

The Speed of Electromagnetic Waves

• The speed of electromagnetic waves in a vacuum is

3.0 × 10⁸ m/s

• This is approximately the same speed as electromagnetic waves in air