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Why do electric field lines end on negative charges?

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In physics, electric field lines are a conceptual tool used to visualize the direction and strength of an electric field. By convention, the direction of the electric field is defined as the direction of the force that would be exerted on a positive test charge.12

Because positive charges repel one another, the field lines around an isolated positive charge radiate outward. Conversely, because a negative charge exerts an attractive force on a positive test charge, the field lines are directed toward it. Therefore, electric field lines are depicted as originating on positive charges and terminating on negative charges.1234

These lines are continuous everywhere except at the charges themselves, which act as the sources or sinks of the field. The number of lines emerging from or entering a charge is proportional to the magnitude of that charge. This construction is particularly useful for representing inverse-square forces, where the density of the lines provides a direct measure of the field's strength at any given point.53