The Electromagnetic Spectrum

• Uses and Applications of EM Waves

  • Radio waves - television, radio, bluetooth
  • Microwaves - satellite, communications, cooking food
  • Infrared waves - electrical heaters, cooking food, infrared cameras
  • Visible light - fibre optic communications
  • Ultraviolet waves - energy efficient light bulbs, security marking, sunbeds
  • X-rays - medical imaging and treatments
  • Gamma rays - sterilising food, treatment of tumours
• Radio waves


  • Low energy waves, not harmful, ideal for radio transmission
• Microwaves


  • Travel in straight lines through the atmosphere, ideal for transmitting signals to satellites in orbit and transmitting them back down to receivers
• Infrared waves


  • Electrical heaters, grills, toasters, etc. glow red hot as the electricity flows through them, transmitting infrared energy that is absorbed by the food and converted back into heat
• Visible light


  • Travels down optical fibres from one end to the other without being lost through the sides
• Ultraviolet waves


  • In energy efficient light bulbs, UV waves are produced by the gas in the bulb when it is excited by the electric current, these UV waves are absorbed by the coating on the bulb, which fluoresces giving off visible light
• X-rays

  • Able to penetrate soft tissue but not bone, a photographic plate behind a person will show shadows where bones are
• Gamma rays


  • The most energetic of all electromagnetic waves, can be used to destroy bacteria and tumours
• Investigate how the amount of infrared radiation absorbed or radiated by a surface depends on the nature of that surface

  1. Take four boiling tubes each painted a different colour: matt black, gloss black, white and silvered

  2. Pour hot water into each boiling tube

  3. Measure and record the start temperature of each tube

  4. Measure the temperature of each tube every minute for 10 min

  5. The tube that cools the fastest, emits infrared energy the quickest
• A common error in this experiment is not having the boiling tubes at the same temperature at the start - a hotter tube will cool quicker initially, which can affect results
• Evaporation from the surface of the water can cause cooling too, which will affect the results. To minimise this, block the top of each tube with a bung or a plug of cotton wool
• Variables


  • The independent variable is the colour of the boiling tube
  • The dependent variable is the temperature change
  • Control variables include volume of water, start temperature and environmental conditions
• Radio Signals


  . Radio waves can be caused by oscillations in electrical circuits, i.e an alternating current

  . The frequency of the radio wave produced matches the frequency of the electrical oscillation. This is how a radio signal is produced

  . When radio waves are absorbed by a conductor they may create an alternating current with the same frequency as the radio wave, this is how the signal is received

  . When this oscillation is induced in an electrical circuit it creates an electrical signal that matches the wave
• Changes in atoms and the nuclei of atoms


  Can result in EM waves being generated or absorbed over a wide frequency range
• Electrons moving between energy levels

  • Generating infrared waves, visible light, ultraviolet waves and X-rays
• Changes in the nucleus of an atom

  • Generating gamma rays
• Ultraviolet waves, X-rays and gamma rays


  • Carry enough energy to have hazardous effects on the human body
• Ultraviolet waves


  Can cause the skin to age prematurely and increase the risk of skin cancer
• X-rays and gamma rays

  Are ionising radiation - they can damage cells by ionising atoms and, if absorbed by the nucleus of the cell, can cause gene mutations and cancer
• Key Point


  . The risk of damage from EM waves depends on the type of radiation and the amount of exposure

  . Radiation doses is a measure of harm based on these two factors. It is measured in Sieverts (Sv)