The attraction between a positive charge and a negative charge arises from the fundamental force known as the electromagnetic force. This force is one of the four fundamental forces of nature, and it is responsible for the interactions between charged particles.
To understand why an additional positive charge attracts a negative charge, we can consider the concept of electric fields. When a positive charge is present, it creates an electric field around itself. The electric field is a property of the charge that extends into space. This electric field exerts a force on any other charged particle in its vicinity.
A negative charge placed in the electric field of a positive charge experiences a force in the direction of the positive charge. This is because the electric field lines emanating from the positive charge extend outward, and the negative charge is influenced by these electric field lines. The force is attractive because the negative charge is pulled toward the positive charge.
This attraction can also be understood in terms of the exchange of virtual photons. According to quantum electrodynamics, charged particles interact by exchanging virtual photons, which mediate the electromagnetic force. In this interaction, the positive charge emits a virtual photon, which is absorbed by the negative charge. The exchange of these virtual photons results in an attractive force between the two charges.
In summary, the attraction between a positive charge and a negative charge is a consequence of the electric field generated by the positive charge and the interaction of the charges through the electromagnetic force.