New trends in physics teaching, v.4; The ... - unesdoc - Unesco

Teacher education: solar energy
the board so that they hold the boiling tubes at the foci of the reflectors. An adjustable leg at
the back allows the plane of the board to be maintained at right angles to the sun’s rays.
Experiments
The reflectors in sunlight act as six identical heat sources. This enables thermal properties of
materials to be compared simultaneously. A straightforward experiment is to put 20, 40, 60,
80, 100 cm3 of water in each of the test tubes, to leave them for about 15 minutes and to note
the different changes in temperature. An extension of this is to use equal masses of different
liquids, for example, kerosene or alcohol or even to use the same mass of iron filings, zinc turnings
and water as an introduction to specific heat capacity. A popular experiment is to compare
the temperature rises of different coloured waters, clear, blackened (with indian ink or aquadag)
red, green, etc. (use poster paints).
Investigations on the effect of covers or diffusers over the reflectors can also be carried out.
Figure 1. Reflector array with electronic thermometer.
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