Required practical - Infrared radiation (AQA GCSE Physics Combined Science): Revision Notes
Required practical - Infrared radiation
This practical helps you understand how different surfaces affect the way materials give out or take in thermal radiation. You'll discover that the colour and texture of a surface makes a big difference to how it behaves with heat.
What you're investigating
The aim is to find out how the nature of a surface affects the rate at which it absorbs or radiates thermal energy.
Different surfaces behave differently with infrared radiation. Some are good at giving out heat, others are good at taking in heat. This practical lets you test this for yourself.
Equipment you need
- Leslie's cube (a metal cube with four different coloured sides)
- Thermometers
- Stopwatch
- Ruler
- Clamp, boss and retort stand
- Hot and cold water
Method 1: How surfaces give out heat (radiating)
This method tests which surfaces are best at emitting (giving out) thermal energy.
Step-by-Step Procedure: Testing Heat Emission
Step 1: Fill the Leslie's cube with hot water at a known temperature
Step 2: Put a bung in the top to keep the heat in
Step 3: Place a thermometer about 10cm away from each side of the cube
Step 4: Take temperature readings every 30 seconds for 5 minutes
Step 5: Do this for all four different surfaces
Method 2: How surfaces take in heat (absorbing)
This method tests which surfaces are best at absorbing (taking in) thermal energy.
Step-by-Step Procedure: Testing Heat Absorption
Step 1: Fill the Leslie's cube with cold water at a known temperature
Step 2: Put a thermometer and bung in the top
Step 3: Heat each side of the cube using a radiant heater from the same distance (about 10cm away)
Step 4: Record how the water temperature changes every 30 seconds
Step 5: Test each surface for the same amount of time
What you'll find (results)
When you plot your results on graphs, you'll see clear patterns:
For giving out heat (Method 1):
- Dull black surfaces cool down the fastest (best emitters)
- Shiny surfaces like silver cool down the slowest (worst emitters)
For taking in heat (Method 2):
- Dull black surfaces heat up the fastest (best absorbers)
- Shiny surfaces heat up the slowest (worst absorbers)
Key Findings
The practical shows that:
- Dull black surfaces are the best at both emitting and absorbing thermal radiation
- Shiny black surfaces are the second best
- White surfaces are third
- Silver surfaces are the worst at both emitting and absorbing
About Leslie's cube
A Leslie's cube is a special piece of equipment made from metal. It has four sides with different surfaces - typically dull black, shiny black, white, and silver. This lets you test all four types of surface at exactly the same temperature and conditions.
Safety Points
- Be careful with hot water - it can scald you
- Make sure you use the same thermometer for each surface test
- Keep the same distance from each surface
- Take the same number of readings for each test to make it fair
Remember!
- Dark, dull surfaces are the best at absorbing and emitting infrared radiation
- Shiny, light surfaces are the worst at absorbing and emitting infrared radiation
- Leslie's cube lets you test four different surfaces fairly
- You need to keep everything the same except the surface type to make it a fair test
- Both absorption and emission follow the same pattern - what's good at one is good at the other