Electromagnetic (EM) Waves (Edexcel IGCSE Science)

Properties of em waves

Spec point — 5.10 · know that light is part of a continuous electromagnetic spectrum that includes radio, microwave, infrared, visible, ultraviolet, x-ray and gamma ray radiations and that all these waves travel at the same speed in free space

• Light is part of a continuous electromagnetic spectrum that consists of the following types of radiation:

  • radio
  • microwave
  • infrared
  • visible
  • ultraviolet
  • x-ray
  • gamma ray

• All waves in the electromagnetic spectrum share the following properties:

  • They are all transverse
  • They can all travel through free space (a vacuum)
  • They all travel at the same speed in free space

The EM spectrum

Spec point — 5.11 · know the order of the electromagnetic spectrum in terms of decreasing wavelength and increasing frequency, including the colours of the visible spectrum

• The types of radiation found in the electromagnetic spectrum have a specific order based on their wavelength (and frequency)

• This order listed above has:

  • radio waves at one end because they have the longest wavelength (and lowest frequency)
  • gamma rays at the other end because they have the shortest wavelength (and highest frequency)

• Wavelength and frequency are inversely proportional to each other, which, according to the Wave equation, means that:

  • as wavelength increases (towards the red end of the spectrum), frequency decreases
  • as wavelength decreases (towards the violet end of the spectrum), frequency increases

Radiation in the EM spectrum, from longest to shortest wavelength

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

The visible light spectrum

• Visible light is the only part of the EM spectrum detectable by the human eye

  • However, it is only a very small part of the whole electromagnetic spectrum
  • In the natural world, many animals, such as birds, bees and certain fish, can perceive beyond visible light and use infra-red and UV wavelengths of light to see

• Each colour within the visible light spectrum corresponds to a narrow band of wavelength and frequency

• The different colours of visible light waves correspond to different wavelengths:

  • red light has the longest wavelength (and the lowest frequency)
  • violet light has the shortest wavelength (and the highest frequency)

The colours of the visible spectrum

The colours of the visible spectrum: red has the longest wavelength; violet has the shortest

Exam Hint See if you can make up a mnemonic to help you remember the order of the colours of visible light in the EM spectrum!.

One possibility is:

Raging Martians Invaded Venus Using X-ray Guns

To remember the colours of the visible spectrum you could remember either:

• The name “Roy G. Biv”
• Or the saying “Richard Of York Gave Battle In Vain”

You could even combine both to have a mega mnemonic:

Raging Martians Invaded Roy G. Biv Using X-ray Guns!

The electromagnetic spectrum is usually given in order of decreasing wavelength and increasing frequency i.e. from radio waves to gamma waves

Remember:

• Radios are big (long wavelength)
• Gamma rays are emitted from atoms which are very small (short wavelength)