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 small 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. 

You can usually make some guesses as to the approximate
magnitude of the force too, so you can draw arrows of appropriate
lengths. 



Force due to a Single Point Positive Charge 

Wherever the test charge (represented by the red dot) 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
as shown below. 





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. 

However, we can still make some reasonable approximations as
stated above. 



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



and, using the same ideas we can predict that the shape of the
field in the vicinity of two similar charges of equal
magnitude would be as shown in the next diagram. 



Notice that, at the centre of this field, there is a place where
the magnitude of the electric field strength is zero. 

This is called a neutral point. 
