Uses of EM Waves

• Radio waves


  EM radiation with wavelengths longer than about 10 cm
• Long-wave radio waves


  • Wavelengths of 1-10 km
  • Can be transmitted from one location and received halfway round the world
  • Can diffract (bend) around the curved surface of the Earth, hills, and into tunnels
• Short-wave radio signals


  • Wavelengths of about 10 m-100 m
  • Can be received at long distances from the transmitter by reflecting off the ionosphere
• Medium-wave signals


  • Can also reflect from the ionosphere, depending on atmospheric conditions and time of day
• Radio waves used for TV and FM radio

  • Have very short wavelengths
  • Require direct line of sight between transmitter and receiver, do not bend or travel far through buildings
• Microwaves


  Used by satellites for communication, can pass easily through the Earth's watery atmosphere
• Satellite communication


  1. Signal from transmitter is sent to satellite

  2. Satellite receives and transmits signal back to Earth

  3. Signal is received on the ground with a slight time delay
• Microwave ovens


  Microwaves are absorbed by water molecules in food, causing them to heat up and transfer energy to the rest of the food
• Infrared radiation


  Given out by all objects, hotter objects give out more IR radiation
• Infrared cameras


  1. Detect IR radiation and turn it into an electrical signal displayed as a picture

  2. Hotter objects appear brighter
• Absorbing IR radiation


  Causes objects to get hotter
• Fibre optic cables


  Thin glass or plastic fibres that can carry data as pulses of visible light, using reflection to keep the light travelling along the fibre
• Fluorescence


  Property of certain chemicals where UV radiation is absorbed and visible light is emitted
• 1. rays


  Pass easily through flesh but not through denser materials like bones or metal, allowing X-ray images to be taken
• Gamma rays


  Used in radiotherapy to kill cancer cells, and as medical tracers
• Both X-rays and gamma rays can be harmful, so precautions are taken to minimize exposure