EM Waves

• What must an object do to maintain a constant temperature?

  Radiate the same average power it absorbs
• What happens if an object absorbs more power than it emits?

  The temperature will increase
• What occurs if an object absorbs less power than it emits?

  The temperature will decrease
• What maintains the temperature of the Earth?

  Energy received and emitted from the sun
• What type of radiation from the sun reaches the Earth?

  Short-wavelength Infra-red radiation
• What happens to the energy absorbed by the Earth?

  It is re-emitted as longer-length IR radiation
• How does the atmosphere affect the Earth's temperature?

  It absorbs longer-length IR radiation
• What is the danger of higher frequency EM waves?

  They can mutate and damage cells
• What effect do microwaves have on body cells?

  Internal heating of body cells
• What can Infra-red radiation cause?

  Skin burns
• What damage can UV radiation cause?

  Damage to surface cells and eyes
• What are the effects of X-ray and Gamma radiation?

  Mutation or damage to cells in the body
• What are the uses of the EM spectrum?

  • Radio: Communications, satellite transmission
  • Microwave: Cooking, communication
  • Infra-red: Cooking, thermal imaging, short-range communication, optical fibres
  • Visible: Vision, photography, illumination
  • UV: Security marking, fluorescent lamps, disinfecting water
  • X-ray: Observing internal structures, airport/medical scanners
  • Gamma: Sterilising food/medical equipment, treating cancer
• What do all electromagnetic waves transfer?

  Energy from source to observer
• What type of waves are electromagnetic waves?

  Transverse waves
• What is the speed of EM waves in a vacuum?

  They all travel at the same speed
• Do EM waves need particles to move?

  No, they do not need particles
• How do materials interact with EM waves?

  Depending on the wavelength
• What happens to wavelength and frequency as speed is constant for EM waves?

  As wavelength decreases, frequency increases
• What happens to energy as frequency increases?

  The energy of the wave increases
• What happens to radiation emitted by bodies at higher temperatures?

  More intense and more wavelengths are emitted