Question

A thermoelectric thermometer is made of copper iron thermocouple. One junction is placed in melting ice and the other is placed in a bath, whose temperature is continuously increased from $0^{0}C$to ${600}^{0}C$ . The current in the galvanometer

• A. Remains constant
• B. Constantly goes on increasing
• C. First increases and then decreases to zero
• D. First increases, becomes maximum and then decreases to zero and finally reverse its direction

Answer 1

Answer: (D)

First increases, becomes maximum and then decreases to zero and finally reverse its direction

In the Cu Fe thermocouple as the temperature of the hot junction is increased with the cold junction at a fixed temperature, the thermo emf increases until a maximum temperature called the neutral temperature and galvanometer current increases first.

A further increase in temperature will make the emf fall until the temperature becomes zero known as the temperature of inversion.

If ${\theta }_c$ is the temperature at the cold junction, ${\theta }_n$ is the neutral temperature and ${\theta }_i$, the inversion temperature then

${\theta }_n=\frac{{\theta }_i+{\theta }_c}{2}$