Question

A thermocouple is made from two metals, Antimony and Bismuth. If one junction of the couple is kept hot and the other is kept cold then an electric current will

A) Flow from Antimony to Bismuth at the cold junction
B) Flow from Antimony to Bismuth at the hot junction
C) Flow from Bismuth to Antimony at the cold junction
D) Not flow through the thermocouple

Answer 1

Hint: A thermocouple is a thermoelectric device used for measuring the temperatures. It is a type of sensor used for measuring the temperature in the form of an electric current. It consists of two wires of different metals connected with the voltages.

Complete step by step answer:
The two metals in the thermocouple are joined in such a way that two junctions are formed. They are connected through welding. When there is a temperature difference at the junction of two different metals, then this temperature difference results in thermoelectric voltages.

In thermocouples, electric current flows from the metal having high voltage to the metal having a low voltage. Antimony has a lower thermoelectric voltage than Bismuth. Therefore, current at the cold junction will flow from Antimony to Bismuth.

Since current flows from antimony to bismuth at the low junction, therefore option A is the right answer.

Note:
It is to be noted that in thermocouple, the two metals used will always be different. This is because different metals generate different amounts of heat at different temperatures. If the metals used will be the same, then there will be no temperature difference. This temperature difference is responsible for the flow of current in the circuit. Also, it is important to note that the metal wires used across the junction should be placed at a distance from each other except at the junction. This is because if they come in contact with each other, then false reading of temperature will be obtained.