A test charge is a hypothetical charge with a magnitude so small that its presence does not affect the electric field in which it is placed. It is used to measure the electric field strength and direction at a point in space without disturbing the field itself.
Electric field lines are a visual representation of the electric field around charged objects, illustrating the direction and relative strength of the field. They originate from positive charges and terminate at negative charges, with their density indicating the field's magnitude.
Electric force is a fundamental interaction between charged particles, described by Coulomb's law, which states that the force between two charges is directly proportional to the product of their magnitudes and inversely proportional to the square of the distance between them. This force can be either attractive or repulsive depending on the nature of the charges involved, and it plays a crucial role in the structure of atoms and the behavior of matter at the atomic and molecular levels.