Thermoelectric phenomena: Which named effect relates the absorption or evolution of heat at the junctions of a thermocouple directly to the electric current flowing in the circuit?

Introduction / Context:
Thermoelectric devices rely on several coupled effects. Distinguishing Seebeck, Peltier, Thomson, and Joule effects helps in understanding both sensing (thermocouples) and active thermal control (thermoelectric coolers). The question targets which effect ties heat absorption/evolution at junctions to electric current.

Given Data / Assumptions:

• Two dissimilar conductors or semiconductors form junctions.
• A current is driven through the circuit.
• We observe heating at one junction and cooling at the other.

Concept / Approach:

Peltier effect: Heat is absorbed at one junction and released at the other when current flows through a junction of dissimilar materials; the heat rate is proportional to current. Seebeck effect: A temperature difference at the junctions generates an emf (basis of thermocouples). Thomson effect: Heat is absorbed or evolved along a single conductor carrying current in the presence of a temperature gradient. Joule effect: Resistive heating proportional to I^2R everywhere in the conductor.

Step-by-Step Solution:

Verification / Alternative check:

Thermoelectric coolers (TECs) leverage the Peltier effect to pump heat; reversing current swaps hot/cold sides—direct evidence of the effect described.

Why Other Options Are Wrong:

Seebeck: Temperature gradient causes emf, not heat flow due to current at junctions. Thomson: Distributed effect along a conductor, not localized at junctions. Joule: Non-directional resistive heating not specific to dissimilar junctions.

Common Pitfalls:

Confusing Seebeck (sensing) with Peltier (active heating/cooling); overlooking that Joule heating always adds heat, whereas Peltier can remove heat at a junction.

Final Answer:

Peltier effect