CP5: light and the electromagnetic spectrum

• what are the uses of radio waves?

  communication, broadcasting, radar, medical imaging

  long wavelength

  low frequency

  low energy

  Transmitted easily through air

  Do not cause damage if absorbed by the human body

  Can be reflected to change their direction
• what are the uses of microwaves?

  Cooking, heating, communication, radar technology.

  Low frequency

  long wavelength

  low energy

  Intense sources of microwaves can be dangerous through internal heating of body cells.

  Microwaves pass easily through the atmosphere, so they can pass between stations on Earth and satellites in orbit.
• what are the uses of infrared?

  Thermography, night vision.

  long wavelength

  low frequency

  low energy

  The heating effect of IR can cause burns to the skin.

  Infrared light has frequencies which are absorbed by some chemical bonds. The internal energy of the bonds increases when they absorb infrared light, which causes heating.

  All objects emit infrared light.
• what are the uses of visible light?

  Illumination, fibre optic communications, and vision.

  In fibre optic communications, where coded pulses of light travel through glass fibres from a source to a receiver.
• what are the uses of ultraviolet?

  Sterilization, disinfection, tanning, fluorescence.

  short wavelength

  high frequency

  high energy

  Ultraviolet light in sunlight can cause the skin to tan or burn.
• What are the uses of x rays?


  Imaging, medical diagnosis, security screening.

  Short wavelength

  high frequency

  high energy
• What are the uses of gamma rays?

  Medical imaging, cancer treatment.

  Shortest wavelength

  highest frequency

  highest energy
• what happens when people have excessive exposure to microwaves?

  internal heating of body cells
• what happens when people have excessive exposure to infrared?

  skin burns
• what happens when people have excessive exposure to ultraviolet ?

  damage to surface cells and eyes causing skin cancer and eye conditions
• what happens when people have excessive exposure to x rays and gamma rays?

  mutation or damage to cells in the body
• What are the similarities between all electromagnetic waves?


  • all transfer energy from source to observer
  • All transverse waves
  • All travel at same speed in a vacuum
• what are the main groups in order of the electromagnetic spectrum and the rhyme?


  • Radio
  • Microwave
  • Infrared
  • Visible light spectrum
  • Ultraviolet
  • X ray
  • Gamma ray

  Red Martians invaded Venus using x ray guns
• which way does the wavelength decrease?


  • Left to right
  • Radio highest
  • Gamma lowest
• which way does frequency decrease?


  • right to left
  • gamma ray has highest
  • radio has lowest
• do EM waves need particles to move?


  no
• in space what happens to EM waves?


  they have the same velocity - speed of light
• what is the relationship between wavelength and frequency?


  inversely proportional as wavelength decreases frequency increases
• what is the relationship between frequency and energy of wave?


  Directly proportional - as frequency increases so does energy of wave
• what do all bodies emit?


  radiation - higher the temperature the more intense and more wavelengths will be emitted
• what is the rule about radiation, power and temperature?


  must radiate the same average power it absorbs to stay at a constant temperature
• What happens if a material absorbs more power than it emits?

  Temperature will increase
• what happens if a material absorbs less power than it emits?

  temperature decreases
• how is the temperature of earth controlled?

  by the amount of energy received and emitted form the sun
• how is temperature on earth controlled (method)?

  • short wavelength infrared radiation from sun to earth
  • some reflected by atmosphere - most reaches surface
  • energy gets absorbed and remitted as long wavelength infrared radiation
  • this is absorbed by the atmosphere
• what are the dangers of the EM spectrum?

  higher the frequency - more energy - too much exposure - too much energy to cells - causing mutations and possibly cancer
• examples of dangers for each part of the spectrum?

  microwaves - internal heating of body cells

  Infra red - skin burns

  uv - damaged surface cells and eyes - cancer

  X ray and gamma - mutation of cell damage
• what are the uses of each part of the EM spectrum?

  radio - communication and satellite transmission

  microwave - cooking and communication

  IR - cooking, thermal images, short communication

  visible light - vision, illumination and photos

  uv - security, fluorescent lamps and disinfecting water

  x ray - scanners - airport and medical

  gamma - sterilisation of food and medical and cancer treatment
• What are radio waves made of?

  Oscillating electric and magnetic fields
• how do radio waves work?

  • generated by a transmitter and a oscilloscope to read the frequency of the AC determining the frequency of the wave
  • the wave can be detected by a receiver which absorbs and generates another AC which is displayed on another oscilloscope
• What can long wavelength waves do?

  • travel long range
  • bend with the earths curve
• what can short wavelength waves do?

  • travel long and short distances
  • cant bend around the earths curve
  • reflected from ionosphere
• what is the ionosphere?

  electrically charged layer of the atmosphere
• what can very short wavelength waves do?

  • used for tv and radio
  • go directly from the transmitter to the receiver
  • objects can get in the way
• what is the distance of a wave?

  how far it has travelled
• what is the displacement of a wave?

  how far from the equilibrium point a wave has oscillated
• what is the amplitude of a wave?

  the maximum displacement of a wave
• what is the wavelength of a wave?

  a whole oscillation
• what are the features of a transverse wave?

  • perpendicular oscillations to the direction of the wave
  • light and radio
• what are the features of a longitudinal wave?

  • oscillations parallel to the direction of the wave
  • sound and seismic p waves