Infrared

• What do glowing coals emit besides visible light?

  Infrared radiation
• Why can't the human eye see infrared radiation?


  Because infrared radiation is outside the visible spectrum
• What is a Lesley's cube used for?


  To see how much infrared is emitted from different surfaces
• What surfaces are present on a Lesley's cube?


  Shiny metallic, white, shiny black, and matte black surfaces
• How do you ensure repeatable measurements when using a Lesley's cube?


  By keeping the same distance between the Lesley's cube and the infrared detector
• Which surface emits the most infrared radiation according to the experiment?


  The matte black surface emits the most infrared radiation
• What is the order of infrared emission from the surfaces tested?


  Matte black > shiny black > white > shiny metallic
• What can be used if an infrared detector is not available?


  A thermometer with the bulb painted black
• What is the limitation of using a thermometer compared to an infrared detector?


  The resolution of the thermometer is less than that of the infrared detector
• What does the resolution of a measuring device refer to?


  The smallest change that can be detected
• How do you measure the absorbance of infrared by different surfaces?


  By using an infrared heater and two metal plates with different surface paints
• What happens to the temperature of the metal plates as they absorb infrared?


  The temperature of the metal plates increases
• What is recorded to determine how well the plates absorb infrared?


  The time it takes for the Vaseline to melt and the drawn pins to fall off
• Which plate loses the drawn pin first and why?

  The matte black plate loses the drawn pin first because it absorbs more infrared
• What is the relationship between matte black surfaces and infrared radiation?


  Matte black surfaces are better at emitting and absorbing infrared than shiny metallic surfaces
• What happens to infrared radiation when it encounters shiny metallic surfaces?


  Infrared tends to be reflected from shiny metallic surfaces
• What are the key steps in the practical investigation of infrared radiation absorption and emission?


  1. Use a Lesley's cube with four different surfaces.
  2. Fill the cube with hot water.
  3. Point an infrared detector at each surface and record emissions.
  4. Use an infrared heater and metal plates to measure absorbance.
  5. Record the time for Vaseline to melt and pins to fall off.
• What are the differences between matte black and shiny metallic surfaces in terms of infrared radiation?


  • Matte black surfaces:
  • Emit more infrared radiation
  • Absorb more infrared radiation
  • Shiny metallic surfaces:
  • Emit less infrared radiation
  • Reflect infrared radiation