The diagrams show the principle schematics of the three major effects in the thermoelectric field: the Seebeck Effect, the Peltier Effect, and the Thomson Effect. What we aim to explore this time is William Thomson and his great discovery — the Thomson Effect.

William Thomson was born in Ireland in 1824. His father, James Thomson, was a mathematics professor at the Royal Belfast Academical Institution. Later, when James accepted a teaching position at the University of Glasgow, the family moved to Glasgow, Scotland, in 1832 when William was 8 years old.

Thomson entered the University of Glasgow at the age of 10 (don’t be surprised — in that era, Irish universities admitted academically promising young pupils). Around the age of 14, he began studying university-level courses, and at 15, he was awarded the university’s gold medal for an essay titled "The Figure of the Earth".

Thomson later studied at the University of Cambridge, graduating with the second-highest rank in his class. After graduation, he went to Paris, where he conducted experimental research for a year under the guidance of Henri Victor Regnault. In 1846, Thomson returned to the University of Glasgow to serve as Professor of Natural Philosophy (now known as Physics), a position he held until his retirement in 1899.

Thomson was a founding father of the modern physics laboratory at the University of Glasgow. At the age of 24, he published a monograph on thermodynamics and established the "Kelvin temperature scale". At 27, he released his book Treatise on Thermodynamics, laying down the Second Law of Thermodynamics and establishing it as a fundamental law of physics. He co-discovered the Joule-Thomson effect in gas diffusion with Joule. After nine years of effort, he oversaw the completion of the transatlantic submarine cable between Europe and America, which operated stably for a long time, earning him the noble title of "Lord Kelvin".

Thomson's research spanned a wide range of fields throughout his life, with significant contributions to mathematical physics, thermodynamics, electromagnetism, elasticity, ether theory, and earth sciences.

In 1856, using the thermodynamic principles he had established, Thomson conducted a comprehensive analysis of the Seebeck effect and the Peltier effect, establishing a connection between the previously unrelated Seebeck coefficient and Peltier coefficient. He proposed that at thermodynamic zero (0 K), there is a simple proportional relationship between the Peltier coefficient and the Seebeck coefficient. Building on this, he theoretically predicted a new thermoelectric effect: when an electric current passes through a conductor with an uneven temperature distribution, the conductor not only generates irreversible Joule heat but also absorbs or releases a certain amount of heat (known as Thomson heat). Conversely, when the two ends of a metal rod are at different temperatures, a potential difference is formed between the two ends. This phenomenon was later named the Thomson effect, becoming the third thermoelectric effect following the Seebeck effect and the Peltier effect.

That’s the story — let’s highlight the key points!

Q: What are the three major thermoelectric effects?A: The Seebeck effect, also known as the initial thermoelectric effect, refers to the thermoelectric phenomenon where a potential difference is generated between two different electrical conductors or semiconductors due to a temperature difference between them.

The Peltier effect, also known as the secondary thermoelectric effect, occurs when an electric current passes through a junction formed by two conductors A and B. In addition to Joule heat generated by the current flowing through the circuit, a heat absorption or release effect is produced at the junction. It is the reverse reaction of the Seebeck effect. Since Joule heat is independent of the direction of the current, Peltier heat can be measured by passing current twice in opposite directions.

The Thomson effect, also known as the tertiary thermoelectric effect. Thomson proposed that at thermodynamic zero (0 K), there is a simple proportional relationship between the Peltier coefficient and the Seebeck coefficient. Building on this, he theoretically predicted a new thermoelectric effect: when an electric current passes through a conductor with an uneven temperature distribution, the conductor not only generates irreversible Joule heat but also absorbs or releases a certain amount of heat (known as Thomson heat). Conversely, when the two ends of a metal rod are at different temperatures, a potential difference is formed between the two ends.

Q: What is the relationship between these three thermoelectric effects?A: The three thermoelectric effects are interrelated: The Thomson effect describes the phenomenon of potential generation when there is a temperature difference between the two ends of a conductor. The Peltier effect refers to the phenomenon of temperature difference generated at the two ends of a charged conductor (one end generates heat, and the other absorbs heat). Combined, these two effects constitute the Seebeck effect.

In summary, the thermoelectric effect refers to the phenomenon where a potential difference and electric current occur when there is a temperature difference at the junction of two materials. The Seebeck effect converts thermal energy into electrical energy, the Peltier effect enables the mutual conversion between electrical energy and thermal energy, while the Thomson effect describes the thermal effect when an electric current passes through a material.