Temperature measurement with a thermocouple

Principle

If two different metals are in contact, a contact potential results from the different electron affinity of the metals' surfaces. The size of this potential is a function of the temperature since the electron's kinetic energy increases with increasing temperature.
These potentials also occur when the thermocouple is connected to a voltmeter. However, they cancel each other (i.e., they do not falsify the measuring results) if both leads which are connected to the meter are of the same material.
A thermocouple consists of a pair of different metals, e.g. iron and constantan. If the two contact points have different temperatures, the difference between the contact potentials can be measured as thermo potential.

Task

How does a thermocouple work? Construct a thermocouple using iron wire and constantan wire; and investigate how it can be used to measure temperature.

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