Question

(A) Thermo emf depends on nature of metals and temperature of junctions.
(B) By a thermoelectric thermometer we can measure temperature of the sun.

• A. Both A and B are true
• B. Both A and B are false
• C. A is true but B is false
• D. A is false B is true

Answer 1

Answer: (C)

A is true but B is false

Statement A is true:

Thermoemf depends on nature of metals and temperature of junctions.

when the temperature difference between two junctions of a thermocouple changes then the emf produced between them called thermo emf is also changed. also for dissimilar metals the thermo emf produced is also different.

Statement B is false:

By a thermoelectric thermometer we can measure temperature of the sun. A radiation thermometer or a pyrometer can be used to measure very high temperatures such as the temperature of the sun. A thermoelectric thermometer is based on the principe of seebeck effect. A thermo EMF(E) arises when two metal junctions are maintained at different temperatures. Thermo emf is developed by keeping one juction at $0^{\circ }C$ and varies with temperature and for Bismuth-Antimony couple E= 1.2 mv/${}^{\circ }C$.

A potential measuring device such as a potentiometer is used to measure the thermo EMF. Only the linear part of curve is found that ranges from -200${}^{\circ }C$ to -1600${}^{\circ }C$. So, it is used to measure rapidly changing temperature of very small objects.