electromagnetic waves

• Waves may be transverse or longitudinal
• Electromagnetic waves are transverse waves with a wide range of properties and uses
• Sound waves are longitudinal waves
• Transverse waves


  Vibrations or oscillations are changes in electrical and magnetic fields at right angles to the direction of wave travel
• Electromagnetic waves


  Transverse waves caused by oscillations in an electromagnetic field
• Electromagnetic waves transfer energy as radiation from the source of the waves to an absorber
• Electromagnetic waves can travel through a vacuum such as in space
• Electromagnetic waves travel at 300 million metres per second (m/s) through a vacuum
• Electromagnetic spectrum


  A continuous series of waves arranged in order of wavelength or frequency
• Groups in the electromagnetic spectrum

  • Waves with very short wavelength, high frequency and high energy
  • Waves with very long wavelength, low frequency and low energy
• Visible light contains all the frequencies that can be detected by the human eye, with red light having the lowest frequencies and violet light having the highest frequencies
• Transverse waves


  Waves where the oscillation is perpendicular to the direction of wave propagation
• Longitudinal waves


  Waves where the oscillation is parallel to the direction of wave propagation
• Electromagnetic waves


  Transverse waves with a wide range of properties and uses
• Sound waves


  Longitudinal waves
• The behaviour of an electromagnetic wave in a substance depends on its frequency
• The differing behaviours of different groups in the electromagnetic spectrum make them suitable for a range of uses
• Radio waves


  • Transmitted easily through air
  • Do not cause damage if absorbed by the human body
  • Can be reflected to change their direction
• Radio waves


  Used for communication such as television and radio
• Radio wave production


  Oscillations close in electrical circuits
• Conductor


  Material which allows charge to move easily through it
• Alternating current


  Electric current that regularly changes its direction and size
• Information is coded into the radio wave before transmission, which can then be decoded when the wave is received
• Microwaves


  Used for cooking food and for satellite communications
• Microwaves


  High frequency microwaves have frequencies which are easily absorbed by molecules in food, increasing their internal energy and causing heating
• Microwaves


  Pass easily through the atmosphere, so can pass between stations on Earth and satellites in orbit
• Infrared light


  Used by electrical heaters, cookers for cooking food, and by infrared cameras which detect people in the dark
• Infrared light


  Has frequencies which are absorbed by some chemical bonds, increasing their internal energy and causing heating
• Infrared light


  All objects emit infrared light, which can be detected by infrared cameras for 'thermal imaging'
• Visible light


  The light we can see, used in fibre optic communications where coded pulses of light travel through glass fibres