Electromagnetic (EM) Waves (OCR Gateway GCSE Physics)

• 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

v = fλ

• Where:
  • v = speed of the wave in metres per second (m/s)
  • f = frequency of the wave in hertz (Hz)
  • λ = wavelength of the wave in metres (m)
• Since all electromagnetic waves travel at the speed of light, c, this is constant
  • Therefore, in the equation, in keeping v constant, if f increases then λ must decrease

Relationship between wavelength and frequency

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

• The electromagnetic spectrum is arranged in a specific order based on the wavelengths or frequencies
• The main groupings of the continuous electromagnetic (EM) spectrum 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)

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

• Visible light is defined as the range of wavelengths which are visible to humans
• Visible light is the only part of the spectrum detectable by the human eye
  • However, it only takes up 0.0035% of the whole electromagnetic spectrum

• In the natural world, many animals, such as birds, bees and certain fish, are able to perceive beyond visible light and can see infra-red and UV wavelengths of light
• The different colours of waves correspond to different wavelengths:
  • Red has the longest wavelength (and the lowest frequency and energy)
  • Violet has the shortest wavelength (and the highest frequency and energy)

Colours of the visible spectrum with increasing wavelength

• Wavelength and frequency are inversely proportional, this means that:
  • An increase in wavelength is a decrease in frequency (towards the red end of the spectrum)
  • A decrease in wavelength is an increase in frequency (towards the violet end of the spectrum)

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