uses of EM waves

• Microwaves are used by satelites:

  • communication to and from satelites uses microwaves
  • they can pass easily though the ionosphere
  • For a satelite TV, the signal from the transmitter is picked up by a satelite dish orbiting the earth. It then transmits the signal back to Earth in a different direction, where it's received by a satlite dish. There is a slight time delay between the signal being sent and received because of the long distance the signal has to travel
• Microwave ovens Also use microwaves:

  • in microwave overs, the microwaves are absorbed by water molecules in food
  • the microwaves penetrate up to a few cm into the food before being absorbed and transfering the energy they are carrying to the water molecules in the food, causing the water to heat up
  • The water transfers this energy into the rest of the food, cooking it
• Ir radiation can be used to increase or monitor temp

  • the hotter the object, the more Ir radiation it gives out
  • IR cameras can be used to detect where heat is being lo st
  • Absorbing IR radiation causes objects to get hotter - Food can be cooked, and Electric heaters work the same was
• Fibre optic Cables:

  • thin glass or plastic fibres that carry data over long distances as pulses of visible light
  • they work because of reflection. the light rays are bounced back and forth until they reach the end of the fibre
  • light is not easily absorbed or scattered as it travels along a fibre
  • Visible light is easy to refract enough so that it remains in the fibre
• X-rays and Gamma Rays are used in medicine

  • xrays pass easily through flesh, but not through harder things like bones or metal
  • Xrays and gamma rays can also be used to treat people with cancer because high doses of these rays kill living cells
  • Gamma radiation can be a medical tracer (inject it and follow it around the body)
  • lead aprons and lead screens
• Dangers of Em waves:

  • UV radiation damages surface cells
  • X-rays and gamma rays are ionising enough to knock elections off atoms, causing gene mutation or cell destruction and cancer
  • Radiation dose (sieverts) is a measurement of the risk from the body being exposed to different parts of the body
  • Is different for different parts of the body