http://www.mpoweruk.com/images/seebeck.gif
Mark Underwood Physics 212 March 2017
Historically, there are three scientists that made major discoveries in thermoelectricity. Thus, there are three processes named after these scientists that describe how thermoelecticity works.
The first is known as the Seebeck effect, which was discovered by Thomas Seebeck in the 1820s. The Seebeck effect is where a temperature differential in two dissimilar metals can cause an electric potential to form. Both are hot on one end and cold on the other, as shown in the picture. One of these metals has electrons that move to the hot end, and is called the n-type metal. The other metal has positively-charged holes, which are spaces where there are no electrons, that move to the cold end. This is called a p-type metal. This movement of electrons and holes causes a potential to form between the cold ends of the metal. The voltage produced is proportional to the temperature differential, i.e. the bigger the difference in temperature between either side of the metals, the greater the voltage. The constant value that determines at what rate this happens is called the Seebeck Coefficient.
The Peltier Effect, named after the French scientist who discovered it, is the opposite of the Seebeck Effect. He found that an electrical current could be used to create a temperature differential in two dissimilar metals. Depending on which way the current flows in the circuit, the places where the two metals are joined together can be made either hot or cold. Usually, though, it is used to make the junction cold, as shown in the picture on the right. Like the Seebeck Effect, the voltage applied to the metals is proportional to the temperature differential created. The proportionality constant in this case is called the Peltier Coefficient.
Uniting these two effects is the Thomson Effect. Named after the man who is more commonly known as Lord Kelvin, the Thomson Effect shows the relationship between the current flowing in a single piece of metal and the heat it produces or absorbs. This is important because it cuts out the need for a second metal to find the Seebeck and Peltier coefficients. The Thomson Coefficient can be used to compute the other two. The Thomson Effect has no direct applications other than finding the other coefficients.
