TABLE OF CONTENTS A field invariant with time is called a static field. For static fields the time derivatives in Maxwell's equations (2.114a) to (2.114d) vanish and we obtain
| (5.1a) |  |
| (5.1b) |  |
| (5.2a) |  |
| (5.2b) |  |
In the static case electric and magnetic fields are not coupled with each other. The source of the electric field is the electric charge and the source of the magnetic field is the electric current. Since in the static case electric and magnetic fields are not coupled with each other the electrostatic field and the magnetostatic field may be treated independently. Electrostatic phenomena involve time-independent distributions of electric charge and electric field. On the other hand, there are no free magnetic charges. Therefore magnetic phenomena are quite different from electric phenomena. Magnetostatic phenomena involve time-independent distribution of electric current and magnetic field. A detailed treatment of electrostatic and magnetostatic fields is given in [1-5].
An example of an electrostatic problem is an arrangement of two or more conductors insulated from each other at different time-constant potential levels and with no impressed currents. In this case an electric field, but no magnetic field exists. Figure 5.1(a) shows an arrangement of two narrowly spaced conducting plates. The electric field and the stored electric energy are mainly concentrated in the space between the conducting plates. A structure optimized for storing electric energy is called a capacitor. An example for a magnetostatic problem is a conductor coil or solenoid with an impressed time-constant...
