Waves: Required Practical: Infrared.

Question 1

What is a Leslie’s cube used for?

Answer 1

• See how much infrared is emitted from different substances.
• 4 different surfaces.
• ## Shiny Metallic Surface, White surface, Shiny Black surface, Matt black surface.

Question 2

What is the method for this practical?

Answer 2

• Fill the Lesile’s cube with hot water.
• Point an infrared detector at each of the 4 substances and record the amount of infrared emmited.
• IMPORTANT: KEEP THE SAME DISTANCE BETWEEN THE LESLIE’S CUBE AND THE INFRARED DETECTOR.
• Makes measurements repeatable.

Results:

• Matt Black emitts the most.
• Shiny Black.
• White.
• Shiny Metallic.

Question 3

What do you do if you do not have an infrared detector?

Answer 3

• Use a thermometer with the bulb painted black.
• The resolution of the thermometer is less than the infrared detector. (Resolution is the smallest change that can be detected).
• ## We may not be able to detect a large difference between the surfaces using a thermometeer.

Question 4

How do we measure the absorbed amount of infrared by different surafces?

Answer 4

• Infrared heater and 2 metal plates on the sides.
• 1 plate has been painted with shiny metallic paint.
• Other plate has been painted with matt black paint.
• Other side of the plates we use vasaline to attach a drawing pin.
• Switch on the heater and timer.
• The temperature of the metal plates increases as they absorb infrared.
• ## Record the time it takes for the vasaline to melt and drawing pin falls off.

Results:

• Drawing pin falls of the matt black plate first this is because the matt black surface absors more infrared than shiny metallic surfaces.
• Matt black surfaces are much better at emmiting and absorbing infrared then shiny materials.
• Infrared tends to reflect off shiny surfaces.