Читать книгу Introduction To Modern Planar Transmission Lines - Anand K. Verma - Страница 22

In the process of discovery of induction, Faraday introduced the concept of fields, and also suggested that the electric energy resides in the field around the charged body and the magnetic energy resides in the field around the magnetized body. Thus, he viewed that the electric and magnetic energies reside in the space around the charged or magnetized body, not in the charge or magnet.

The field concept has greatly influenced the further development of EM‐theory. The field provided a mechanism of interaction between charged bodies. Using Ampere‐Biot–Savart law of magnetic forces, and electromagnetic induction of Faraday, Neumann in 1845 introduced the concept of the magnetic vector potential to describe the magnetic field. Subsequently, Maxwell showed that the time derivative of computes the induced electric field . Kelvin in 1847 further extended the concept of the magnetic vector potential to compute the magnetic field using the relation . This relation comes as a solution of the Gauss divergence equation due to the closed‐loop of the magnetic field, showing the nonexistence of a magnetic charge. Kelvin further elaborated on the mathematical theory of magnetism in 1851. It is interesting to note that at any location in the space once time‐dependent magnetic vector potential function is known, both the magnetic and electric fields could be computed as,

(1.1.1)

Maxwell shared the views of Neumann and Kelvin. However, time‐retardation was not incorporated in the scalar and vector potentials. In 1867, Lorentz introduced the concept of retardation in both the scalar and vector potentials to develop the EM‐theory of light, independent of Maxwell. The time‐retardation only in the scalar potential was first suggested by Riemann in 1858, but his work was published posthumously in 1867 [J.1, J.2, B.6, B.7].