2. Thomson effect. In a wire in which the temperature varies from point to point (as for example in one whose ends are maintained at different temperatures), the free electron density varies from point to point with the temperature (the free electron density is highest at points where the temperature is lowest). As a consequence of this, differences of potential may be observed along the wire corresponding to the varying free electron density. Each infinitesimal element of a wire of nonuniform temperature is thus a seat of emf, a discovery made by Sir William Thomson (Lord Kelvin). When a current is maintained in a wire of nonuniform temperature, heat is liberated or absorbed at all points of the wire. This heat, called Thomson heat, is proportional to the quantity of electricity passing the section of wire and to the temperature difference between the ends of the section.
Def. Thomson emf, σAdt. If an infinitesimal length of wire A has a temperature difference dt (i.e. dt is temperature difference between the beginning and end of the section), the number of joules of heat absorbed or liberated in this length of wire per coulomb of electricity transferred is called the Thomson emf, σAdt
The total Thomson emf in a wire whose ends are at temperatures t1 and t2 is
The coefficient σA is sometimes called the “specific heat of electricity”.
http://www.solitaryroad.com/c1045.htmlhttps://www.chemguide.co.uk/physical/redoxeqia/introduction.html2. Polarization. As a voltaic cell operates, the positive electrode tends to become coated with an accumulation of tiny bubbles of hydrogen gas. Thus an electrode of hydrogen has been effectively substituted for the carbon electrode we started with. The result is a gradual drop in voltage as the cell operates. The phenomenon is called polarization. To overcome this defect, manufacturers add a depolarizer such as potassium dichromate to the cell. The depolarizer unites chemically with the hydrogen and removes it from the carbon.
