Physicists attempt to work with as few assumptions as possible.
One of the fundamental assumptions is that the interactions of two distinguishable objects are independent of the labels we use to identify them . Hence the electrical force between two charges must be the same regardless of which we call q 1 and which is called q 2 . In order to model the electrical influence of an isolated charge, we resort to a rather fictional scenario. The notion here is that a charged particle has an influence independent of whatever forces are felt by other charges. These flux lines indicate the direction a positively charged test particle would move due to the electric force between it and the configuration charge.