Electric Field Lines for Two Objects on a Frictionless Table

[JessicaHelena]

Homework Statement

In the diagram, two small objects, each with a charge of -4.0nC, are held together by a 0.020 m length of insulating string. The objects are initially at rest on a horizontal, non conducting frictionless table & the effects of gravity on each other are negligible.

(b) Illustrate the electric fiel by drawing electric field lines for the two objects.

What I did and the solution are both attached. However, the problem is I don't understand why the solution has those curvy lines & they don't provide an explanation.

Homework Equations

none?

The Attempt at a Solution

I learned that electric field lines tend to go towards the negative objects and away from the positive objects. But I'm not sure if I've learned anything that helps me think of curvy electric fields...

 

[haruspex]

You can think of each field line as pairing up two equal and opposite quantities of charge, positive at the tail and negative at the head.
If the system under consideration has a net charge this means that some lines are unpaired, so go off to infinity.
The other fact you need is that field lines don't cross. Indeed, they behave as though they repel neighbouring lines in the same direction.
From these you should be able to deduce the sort of arrangement in the diagram.