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Electricity and Magnetism

Electric Field Shapes

Electric fields are often represented by electric lines of force.

A line of force is a line showing the direction of the force acting on a positive charge placed in the field.

The "density" of the lines represents the magnitude of the field strength.

To draw a diagram showing the shape of an electric field, imagine a small positive charge (a test charge) to be placed in the field at different points.

Field due to a single charge

Wherever the test charge is placed, the force will be directed away from the charge (or towards the charge if it is negative). Therefore, in this case, the shape of the field is radial.

Field due to two opposite point charges of equal magnitude

In this slightly more complicated case, a vector addition is needed to predict the direction of the line of force at the point considered.

By considering a number of such additions, we obtain the following shape.

Field due to two similar point charges of equal magnitude

The same process gives the following result.

At the centre of this field is a place where the magnitude of the electric field strength is zero. This is called a neutral point.

Field between two oppositely charged parallel plates

In between the plates the field is uniform except near the ends.

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