Experiments with a thermoelectric generator - results and answers

It is obvious that the temperature sensors do not adequately track the actual temperatures of the plates but it is suggested that a voltage mean be taken from the heating and cooling curves. The centrally placed curve was generated from these data values and is seen to give a good straight-line graph. The reciprocal of gradient yields an output of 22.5 ± 0.5 mV per °C which is close to the manufactures' specification of 2 5mV per °C for a typical cell. (It must be noted that this conversion parameter does vary slightly with the operating temperature of the module. However, over a temperature range of 50 degrees or so, the variation will only be a few parts in a hundred.)

An ideal voltage generator should have a low internal resistance to give significant power output when a load resistor is attached to the output. The internal resistance was found to be approximately 1.8 ohms. The value given by the manufacturer was 1.5 ohms so, again, there is reasonable agreement.

Figure 5: a graph showing output voltage from the thermoelectric generator

Teachers' notes

Safety issues:

• Obviously parts of the thermoelectric generator will be hot so take precaution against burns.
• Students should be aware of the dangers of electricity and the apparatus should be built so as to reduce the risk of electric shock.

Target age groups:
Ages 9 -16 (Key Stage levels 3 and 4)

National curriculum:
The thermoelectric generator experiment is suitable for KS3 or KS4 stages as a demonstration of:
a) Energy conversion
b) Data capture

Reference material
Teachers may find the following reference material useful:-

• R G Chambers (Sept 1977), "Thermoelectric effects and contact potentials (for teachers)"

Physics Education Vol12 No6 pps 374-379

• (April 1988) Reports on the progress in Physics Vol5 No4 pps 459-539
• C Wood (1988), Materials for thermoelectric energy conversion