Whenever two point charges are placed at the end points of a straight line, the electric field is zero. This is known as null points.
The reason for this is that when you place two opposite charges on a screen, the sum of their electric fields is zero at the point where they join. This is the only position where the field vectors can be in completely opposite directions.
This is because the magnitude of the electric field between these two charges must add together at all points along the line that they cross, but it must be in opposite directions when the lines are run between them.
In order to find the sum of these fields at each point, the usual operations that apply to vectors can be applied to them, such as summing and subtracting. This is how we determine the net electric field at each location in space.
When the field lines are spread out at various distances from a source charge, we can use circular cross-sections to determine their strength. These cross-sections represent regions of space that are closer to or further from the charge.
When we draw these circular cross-sections, we find that the field lines are closer together in the regions of space closest to the charge and farther apart in the regions of space farthest from the charge. The density of these field lines reveals information about the quantity of charge on the source charge.
