10 - Infrared

• Investigating how much infrared radiation is emitted by different surfaces:

  1. Fill a Leslie's cube with hot water
  2. Point an infrared detector at each of the four surfaces and record the amount of infrared emitted
  3. Keep the same distance between the Leslie's cube and the infrared detector in order to make the measurements repeatable

  If we do not have an infrared detector then we can use a thermometer with the bulb painted black, however the resolution of the thermometer is less than the infrared detector

  
• A Leslie's cube is used to see how much infrared is emitted from different surfaces. It has four different surfaces including a shiny metallic surface, a white surface, a shiny black surface and a matt black surface (matt means not shiny)
• In terms of infrared emissions, these are our results:

  A) most

  B) least

  C) matt black

  D) shiny black

  E) white

  F) shiny metallic

  
• Measuring the absorption of infrared radiation by different surfaces - experiment:

  1. Set up the apparatus
  2. Switch on the heater and start timing
  3. The temperature of the metal plates increases as they absorb infrared
  4. Record the time it takes for the vaseline to melt and the drawing pins to fall off
• Measuring the absorption of infrared radiation by different surfaces - apparatus:

  • We have an infrared heater and on either side we have two metal plates
  • One plate has been painted with shiny metallic paint whereas the other plate has been painted with matt black paint
  • On the other side of the plates, we have used vaseline to attach a drawing pin

  A) metal plate

  B) infrared heater

  C) drawing pin

  D) shiny metallic surface

  E) matt black surface

  F) drawing pin

  G) metal plate

  
• Measuring the absorption and emission of infrared radiation by different surfaces - results:

  • The drawing pin falls off the matt black plate first because matt black surfaces absorb more infrared than shiny metallic surfaces
  • Therefore matt black surfaces are much better at emitting and absorbing infrared than shiny metallic surfaces
  • Infrared tends to be reflected from shiny metallic surfaces instead