There is a switch on the thermoconverter to alternate the junction plates between the motor fan or a pair of 4mm sockets.
A series of semiconducting junction plates are sandwiched between 2 aluminum heat-conducting plates.
When the 4mm sockets pair are selected and driven with a 5V DC voltage, a temperature difference will be created and conducted by the aluminium plates.
When a temperature difference exists between the 2 sides of the junction plate, electric current is generated to drive a little fan, providing a visual demonstration of the current produced.

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Ltekonline are the manufacturers of Thermoelectric Converter Heat Lab used to demonstrate engineering principles in Engineering Colleges, Engineering Schools and Physics Lab Experiments for Engineering Teaching Lab in Universities