ABSTRACT
Electric fields, magnetic fields and conduction fields (i.e., a region in which an electric current flows) are analogous, i.e., they all exhibit similar characteristics. Thus they may all be analysed by similar processes. In the following the electric field is analysed
Figure 40.1 shows two parallel plates A and B. Let the potential on plate A be CV volts and that on plate B be V volts. The force acting on a point charge of 1 coulomb placed between the plates is the electric field strength E. It is measured in the direction of the field and its magnitude depends on the p.d. between the plates and the distance between the plates. In Figure 40.1, moving along a line of force from plate B to plate A means moving from V to CV volts. The p.d. between the plates is therefore 2 V volts and this potential changes linearly when moving from one plate to the other. Hence a potential gradient is followed which
Figure 40.1 Lines of force intersecting equipotential lines in an electric field
Lines may be drawn connecting together all points within the field having equal potentials. These lines are called equipotential lines and these have been drawn in Figure 40.1 for potentials of 23 V,
1 3 V, 0,
13 V and 23 V. The zero equipotential line represents earth potential and the potentials on plates A and B are respectively above and below earth potential. Equipotential lines form part of an equipotential surface. Such surfaces are parallel to the plates shown in Figure 40.1 and the plates themselves are equipotential surfaces. There can be no current flow between any given points on such a surface since all points on an equipotential surface have the same potential. Thus a line of force (or flux) must intersect an equipotential surface at right angles. A line of force in an electrostatic field is often termed a streamline.
