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Equipotentials and fields

The following diagrams show the arrangement of some electric fields and the accompanying equipotentials. Remember that these diagrams are shown in two dimensions while the actual field lines are in three dimensions and the equipotentials are equipotential surfaces also in three dimensions.

The equipotentials are at right angles to the field lines.

Figure 1 (a) and (b) shows the simplest fields – (a) that round a point charge (known as a radial field because the field lines are extensions of the radius) and (b) that between a pair of parallel plates (known as a parallel field because the field lines are parallel to each other).



Figure 2 (a) and (b) shows the fields and equipotentials related to two charges – (a) similar and (b) opposite charges. Notice that in (a) there is a kind of 'plateau' between the two charges. The field has a definite value here but it changes very slowly. A charge (of either sign) placed at the centre of this plateau would be in equilibrium. In (b) a charge placed anywhere in the field would experience a resultant force and so move at right angles to the equipotentials lines.




Figure 3 shows the field and equipotentials between a single charge and a flat plate. Notice that the field lines meet the plate at right angles – it is an equipotential surface. Any charge placed on the plate would not move.










The final diagram (Figure 4) shows the field lines and equipotentials around a point on a flat surface. This is the situation produced around a lightning conductor. There is an intense field around the point shown by the closeness of the equipotentials there.

 
 
 
© Keith Gibbs 2013