Energy Transferred by Radiation
Energy and Thermal Physics

Further experiments on radiation

Practical Activity for 14-16 PRACTICAL PHYISCS

Class practical

Shows the properties of infra-red radiation.

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

Health & Safety and Technical Notes

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


Pre-focus (P13.5s) torch bulbs (2.37W) are available both vacuum and krypton filled. Distinguishing between these will require a sensitive detector.

Procedure

  1. 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.
  2. 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.
  3. 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.
  4. Put a cheek near a mains lamp and switch it on and off to feel how promptly the radiation reaches the face.

Teaching Notes

  • Step 1 is a version of Leslie's cube and demonstrates the differing amounts of radiation emitted from differently coloured surfaces.
  • In step 2, the matt black can cools down most quickly because more radiation is emitted from it. Cooling curves could be plotted.
  • In step 3 the surface of the gas-filled lamp will be hotter. This is because of the energy transferred through the gas by conduction, although the energy transferred by infra-red radiation will be similar.
  • In step 4 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-tested in April 2006

Energy Transferred by Radiation
appears in the relation ΔQ=PΔt
is a special case of Energy Transferred by Heating
is used in analyses relating to Radiative Heating
IOP DOMAINS Physics CPD programme

Energy CPD videos

Our new set of videos gives teachers and coaches of physics a preview of the training we offer ahead of this term's live support sessions.

Find out more