Weisman-Franz Law
The Weisman-Franz law, formulated by Rudolph Weisman and Julius Franz in the 19th century, states that the electric conductivity of metals increases linearly with absolute temperature. This phenomenon was first observed and formulated in 1841 by the famous English scientist, William Thomson (or Lord Kelvin). The Weisman-Franz law applies to all metals, as well as to certain alloys and semiconductors, provided the electron mean free path is much shorter than the prevailing distances between molecules forming the lattice of a material. While metals obey the Weisman-Franz law, nonmetallic materials may follow different rules.
This law is based on the fact that the electric conductivity of a material is related to the number of charge carriers, their mobility and the scattering of these carriers by the surrounding molecules. As temperature increases, the number of charge carriers increases because of their excitation from the thermal energy, and their mobility increases too. This effectively increases the electric current flowing through the material, hence its electric conductivity. Therefore, the Weisman-Franz law is an expression of the mobility of charge carriers when studying the behavior of materials at different temperatures.
The Weisman-Franz law is also related to the Wiedemann-Franz law, which states that the thermal conductivity of metals increases with increasing electrical conductivity. This relationship was first discovered by Gustav Wiedemann in 1853 and independently by Julius Franz in 1858. Both Weisman and Franz were contributors to the development of this law. The Wiedeman-Franz law is often renamed the Weisman-Franz law since they both were the major contributors to this discovery.
Moreover, the Weisman-Franz law is related to the Fermi-Dirac statistics theory which explains why an increase in temperature causes an increase in electrical conductivity. According to Fermi-Dirac theory, when a material is heated, its atoms start to vibrate faster and electrons are excited from the ground state and start to move in the conduction band. This results in an increased number of charge carriers and hence an increased electrical conductivity.
The Weisman-Franz law can be used to predict the electric conductivity of materials and their behavior at different temperatures. For example, the electric conductivity of a metal increases exponentially as its temperature is raised, due to an increase in the number of charge carriers. Therefore, the Weisman-Franz law is useful in many fields, such as electrical engineering and electronics.
Finally, the Weisman-Franz law is an important example of how temperature is related to electric conductivity. This law provides the basis for many applications in the fields of physics, materials science and engineering. For example, it is used to calculate the performance of electric motors, generators and other electrical machines; to evaluate the thermal properties of solids and alloys; and to design thermoelectric devices. Therefore, this law has had, and will continue to have, a great impact on our understanding of thermoelectricity.
