Question

Thermocouple is based on the principle of
A) Seebeck effect
B) Thomson effect
C) Peltier effect
D) Joule effect

Answer 1

Hint : A thermocouple is an electrical device which is used for measuring the variations in temperature. In recent times thermocouples are called sensors rather than calling them as a device. Because the main function of the thermocouple is to sense the temperature and it needs the help of other instruments for measuring the temperature.

Complete step by step solution:
As told above a thermocouple is a temperature measuring device. So it has to work on some kind of thermoelectric effect. The working principle of the thermocouple is known as the Seebeck effect. The Seebeck effect is named after Thomas Johann Seebeck who discovered this effect in 1821.

According to the Seebeck effect if there are two dissimilar conductors or semiconductors in contact with each other in a closed circuit then the temperature difference between them then an electromotive force is induced within this closed circuit. This phenomenon is utilised in a thermocouple to measure temperature. So, basically, a thermocouple consists of two dissimilar conductors or semiconductors that remain in contact with each other and any temperature difference experienced by these dissimilar conductors induces an electromotive force (E.M.F) within the closed circuit. This electromotive force can be measured by some suitable instruments.

The thermocouple device is provided with a meter gauge to read the temperature readings in $^\circ C$. The meter gauge is calibrated to read the temperature directly by setting the value of $0 ^\circ C$ when there is no current flowing through the thermocouple circuit.

Note: The term calibration or calibrated is used in the above discussion. Many of the students may be unaware of this term. However, it is a very important term when it comes to measurement or metrology. Calibration refers to marking of units on a measurement device to be able to read it on the instrument. For example, the ruler you use for drawing straight lines is calibrated with the units like cm and inches to measure the length of the line.