The thermocouple produces
a voltage proportional to the temperature difference between the heated end of
a conductor and its cold end. To measure that voltage the conductor must be
connected to a circuit.
To make the circuit
another wire of a different material is connected to the heated end of the
original conductor (a hot junction is formed) the other end of both conductors
are attached to a millivolt meter which forms the
cold junction.
Note this is required if
you want to use the thermocouple to sense temperature, the thermocouple
principle simple needs the two dissimilar metal conductors to be connected
together at a hot and cold junction !
The correct answer is two
dissimilar metal joined together at one end (called the hot junction or
measuring end) all other answer given refer to identical metals or a single
wire which are wrong.