4.Main Content
experiments
Further experiments on radiation
Class experiment
Shows the properties of radiant energy.
Apparatus and materials
For each group of students:
- Mains lamps and holders, gas-filled and vacuum-filled (60 watt). Please note this piece of apparatus is very difficult to find.
- Copper calorimeter, large or a steam chest
- Immersion heater (mains powered)
- Vegetable black
- Thermometer (0°-100°C)
- Paper, white
Technical notes
Pre-focus (P13.5s) torch bulbs (2.37W) are available both vacuum and krypton filled. Distinguishing between these will require a sensitive detector.
Safety
If mains lamps are used, the holders should be the 'safety pattern' where the contacts are isolated when the lamp is removed.
Read our standard health & safety guidance
Procedure
a Keep some water boiling inside a copper box using an immersion heater. Alternatively the box can be kept at 100'C by passing steam through it. One face is shiny; one face is dull black having been coated with vegetable black, one face is covered with white paper. Use the back of the hand to compare the radiation.
b Put a thermometer (0°-100°C) in a metal container filled with boiling water, and observe the rate of cooling. Do this first with a well-polished container. Then with a layer of vegetable black painted on the outside.
c Switch on a 60 watt gas-filled mains lamp and a 60 watt vacuum-filled mains lamp near each other. Ask students to decide, as a detective problem, which of the two has gas inside.
d Put a cheek near a mains lamp and switch it on and off to feel how promptly the radiation reaches the face.
Teaching notes
1 Step a is a version of Leslie's cube and demonstrates the differing amounts of radiation emitted from differently coloured surfaces.
2 In step b, the matt black can cools down most quickly because more radiation is emitted from it. Cooling curves could be plotted.
3 In step c the surface of the gas-filled lamp will be hotter. This is because of the energy conducting through the gas, although the energy radiated will be similar.
4 In step d the time lag is too short to distinguish because the radiation travels at a very high speed. (The speed of light.)
This experiment was safety-checked in April 2006