Thermocouples:

Whenever a metal is subjected to thermal gradient then it will generate voltage. This is known as Thermoelectric effect or See back effect. Any attempt to measure this voltage necessarily involves connecting another conductor to the "hot" end. This additional conductor will then also experience the temperature gradient, and develop a voltage of its own which will oppose the original. Fortunately, the magnitude of the effect depends on the metal in use. Using a dissimilar metal to complete the circuit will have a different voltage generated, leaving a small voltage difference available for measurement, which increases with temperature. This difference can typically be between 1 to about 70 microvolts per degree Celsius for the modern range of available metal combinations.

In our apparatus we used K-type thermocouple made of Chromel and Alumel wires. These two wires are twisted at one end and are insulated with the help of glassy sleeves. The twisted end is applied to the place whose temperature is needed to be sensed with the help of nut screw and washer.