A

Step 1: Understand the scenario described in the question. When two ends of a conductor are at different temperatures, a voltage is generated across the conductor due to the temperature difference.
Step 2: Identify relevant phenomena:
- Seebeck Effect: This is the phenomenon where a voltage is generated in a circuit made of two different materials when there is a temperature difference between the junctions. This voltage is known as the Seebeck electromotive force (e.m.f.).
- Peltier Effect: This occurs when current flows through a circuit of two different conductors at a junction, causing heating or cooling at the junction due to the electric current, not due to temperature difference directly.
- Thomson Effect: This effect describes the heating or cooling of a current-carrying conductor in a temperature gradient, but again it doesn't directly represent the e.m.f. generated due to just temperature difference.
Conclusion: The described situation aligns with the Seebeck effect, where the e.m.f. is generated due to a thermal gradient in the conductor.
Therefore, the correct answer is Option A: Seebeck electro motive force (e.m.f.).