the electromagnetic spectrum

• electromagnetic waves are transverse
• all electromagneticwaves travel at the same speed 3 × 10 $^8$ m/s
• the em spectrum extends from low frequency , long wavelengths and low energy to high frequency , short wavelengths and high energy
• the human eyes can only detect visible light
• the wavelength of an em wave affects how it is absorbed, transmitted , reflected or refracted by different substances , this affects its use
• raging martians invade venus using xray guns
• RADIO WAVES

  • television , radio and bluetooth
  • radio waves are low energy and therefore not harmful
• microwaves

  • satellite communication and cooking food
  • microwaves travel in straight lines through the atmosphere
  • this makes them ideal for transmitting signals to sattelite in orbit and transmitting them back down to receptors
• infared waves

  • electrical heaters , cooking food, infared cameras and remote controls
  • they glow red when electricity flows through them
  • this transmits infared energy that is absorbes by food and converted back to heat
• visible light

  • fibre optic communication and photography
  • visible light travels down optical fibres from one end to the other withought being lost through the sides
• ultraviolet waves

  • energy efficient bulbs , security marking and sunbeds
  • in energy efficient light bulbs , uv waves are produced when it is excited by electrical current
  • the waves are then absorbed by the coating on the bulb which fluoresces giving off visible light
• x-rays

  • medical imaging and treatments
  • x-rays are able to penetrate soft tissue but not bone
  • a photographic plate behind the person will show where the bones are
• gamma rays

  • sterilisation and treatment of tumours
  • gamma rays are the most energetic and can be used to destroy bacteria and tumours
• radio signals

  • radio waves are caused by oscillations in an electrical circuit ( ac current )
  • the frequency of the radio wave produced matches the frequency of the electrical oscillation
  • the radio waves are absorbed by a conductor they may create an alternating current with the same frequency as the wave , this is how a signal is recieved
  • when this oscillation is induced in an electrical circuit it created an electrical signal that matched the wave
• hazards of em waves

  • changes in atoms or nuclei can generate or absorb em waves
  • electrons moving between energy levels as a result of heat or electrical excitation can generate waves eg. infared
  • changes in the nucleus eg. an unstable nucleus can give out excess gamma rays
• uv waves , x-rays and gamma rays can carry enough energy to give hazardous effects eg

  • uv waves cam cause the skin to age prematurely increasing risk of skin cancer
  • xray and gamma rays are ionising