Electromagnetic (EM) Waves (OCR GCSE Physics A (Gateway))

Range of EM Waves

• 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 EM Spectrum

• 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

• 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