Req Pratical 10: Infrared

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

  Infrared radiation is outside the visible spectrum
• What is a Lesley's cube used for in this practical?

  To measure infrared emission from surfaces
• What surfaces are present on a Lesley's cube?

  Shiny metallic, white, shiny black, matte black
• How do you ensure repeatable measurements in the experiment?

  Keep the same distance between the cube and detector
• Which surface emits the most infrared radiation according to the experiment?

  Matte black surface
• What is the order of infrared emission from the surfaces tested?

  Matte black, shiny black, white, shiny metallic
• What alternative method can be used if an infrared detector is unavailable?

  Use a thermometer with a blackened bulb
• What is the resolution of a thermometer compared to an infrared detector?

  The thermometer has lower resolution
• Why might a thermometer not detect differences between surfaces effectively?

  It has lower resolution than an infrared detector
• What equipment is used to measure infrared absorbance in the second part of the experiment?

  An infrared heater and two metal plates
• What are the two types of paint used on the metal plates?

  Shiny metallic paint and matte black paint
• What happens to the temperature of the metal plates when the infrared heater is switched on?

  The temperature increases as they absorb infrared
• What does the melting of Vaseline indicate in the experiment?

  How quickly the plates absorb infrared radiation
• Which plate loses the drawn pin first?

  Matte black plate
• Why do matte black surfaces perform better in absorbing infrared?

  They are designed to absorb more infrared radiation
• How do shiny metallic surfaces interact with infrared radiation?

  They tend to reflect infrared radiation
• What type of questions can be expected on this practical?

  Questions related to infrared absorption and emission
• What are the steps to investigate infrared radiation absorption and emission?

  1. Use a Lesley's cube with four surfaces.
  2. Fill the cube with hot water.
  3. Point an infrared detector at each surface.
  4. Record the infrared emitted from each surface.
  5. Use an infrared heater and metal plates to measure absorbance.
  6. Record the time for the Vaseline to melt.
• What are the characteristics of surfaces in terms of infrared radiation?

  • Matte black surfaces: Best at absorbing and emitting infrared
  • Shiny black surfaces: Good at emitting, less than matte
  • White surfaces: Moderate emission
  • Shiny metallic surfaces: Least emission, reflect infrared