Question

In a metal with positive Thompson coefficient, current is passed from the lower temperature to higher temperature side. The heat will be
A. absorbed
B. constant
C. evolved
D. either B or C

Answer 1

Hint: When current flow through unequally heated conductors, i.e. the entirety of the body is not at the same temperature, heat energy is absorbed or evolved throughout the body of the conductor. The potential at a point of lower temperature is lower than at the point at a higher temperature which is at the higher potential. In the given question the current is passed from lower temperature to higher temperature of the metal. In this case, work has to be done. And it will require energy in some form.

Complete answer:
When the points of a conductor are at different potentials then there is a potential difference due to the unequal heating of the conductor. The potential at a point whose temperature is colder is lower than that of the hotter point. This is called Thompson’s Effect.
The evolution of heat when current is passed from hotter end to the colder end and the absorption of heat when current is passed from colder end to hotter end is called Positive Thomson's effect.
Heat energy evolved or absorbed when one Coulomb of charge (1 ampere current in 1 sec) flows through the metal between two points whose temperature difference is 1 degree Celsius is called Thomson coefficient. It is denoted by σ.
In our question, it is given that the metal has a positive Thompson coefficient thus it will affect Positive Thomson's effect. The current is passed from lower temperature to higher temperature of the metal. In this case, work has to be done. Thus, energy will be needed and that energy will be provided by heat. Therefore, Heat will be Absorbed.

So, the correct answer is “Option A”.

Note:
There are two types of Thompson’s effect, namely, positive and negative. In positive Thompson’s effect, when current is passed from the hotter end to the colder end heat is evolved and vice versa. Meanwhile, in negative Thompson’s effect, the hot end is at a lower potential and when current flows from hotter to colder end, heat is absorbed.