Radiation waves

• Infrared radiation


  Radiation emitted from the surface of an object
• Infrared radiation


  • The hotter an object is, the more infrared radiation it radiates in a given time
  • An object that's hotter than its surroundings emits more IR radiation than it absorbs, and it cools
  • An object that's cooler than its surroundings absorbs more IR radiation than it emits, and it warms up
  • Objects at a constant temperature emit infrared radiation at the same rate that they are absorbing it
• Surfaces and colors


  • A black surface is better at absorbing and emitting radiation than a white one
  • A matt surface is better at absorbing and emitting radiation than a shiny one
• Investigating emission with a Leslie cube

  1. Place an empty Leslie cube on a heat-proof mat

  2. Fill the Leslie cube with boiling water

  3. Wait for the cube to warm up

  4. Hold a thermometer against each of the four vertical faces of the cube

  5. Hold an infrared detector a set distance away from one of the cube's vertical faces and record the amount of IR radiation it detects

  6. Repeat this measurement for each of the cube's vertical faces, positioning the detector at the same distance each time
• You should find that you detect more infrared radiation from the black surface than the white one, and more from the matt surfaces than the shiny ones
• Black body


  An object that absorbs all of the radiation that hits it, with no radiation reflected or transmitted
• Black body radiation


  • The intensity and distribution of the wavelengths emitted by an object depend on the object's temperature
  • As the temperature of an object increases, the intensity of every emitted wavelength increases, but the intensity increases more rapidly for shorter wavelengths than longer wavelengths
  • This causes the peak wavelength (the wavelength with the highest intensity) to decrease as the object gets hotter
• The overall temperature of the Earth depends on the amount of radiation it reflects, absorbs and emits
• During the day


  Lots of radiation (like light) is transferred to the Earth from the Sun and absorbed, causing an increase in local temperature
• At night


  Less radiation is being absorbed than is being emitted, causing a decrease in the local temperature
• Changes to the atmosphere can cause a change to the Earth's overall temperature. If the atmosphere starts to absorb more radiation without emitting the same amount, the overall temperature will rise until absorption and emission are equal again
• The peak wavelength of radiation you emit is about 10 μm