Welcome to practical physicsPracticle physics - practical activities designed for use in the classroom with 11 to 19 year olds
 

Further experiments on radiation

Class practical

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

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.

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

 

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