Electric potential is amount of work required to move a unit charge from a reference point or surface to a specified point in an electric field. Accordingly, the energy possessed by a charged particle is due to its position with respect to the electric field. Electric potential is a scalar quantity and can result from the introduction of a particle into an electric field produced by a source of potential difference such as a battery, or by another nearby charged particle.
Electric potential can be compared to the gravitational potential energy of an object in a gravitational field. Just as the gravitational field results in a force on an object with mass or momentum, an electrical field results in a force upon a charge. The work done by the electric field depends only on the initial and final positions of the object, not the path followed by the object between the two points. In addition, just as a gravitational field results in a gravitational potential energy for an object relative to a specified surface (e.g., the surface of Earth), an electric field results in charged particle's electric potential energy. The magnitude of the electric potential is dependent upon the particle's charge and the electric field strength. If the particle has no charge then an electric field has no effect on it.
Relative to a particle, A, when an electric field exists due to another charged particle, B, the electric potential of particle A is dependent upon the charges of the particles and the distance between the two particles. The point of zero electric potential is taken to be when particle B is at infinite distance from particle A. If the two particles are of the same sign then the electric potential is positive because like charges repel one another.
The electric potential at a distance r from an isolated point charge Q, or from the center of a equipotential sphere, is directly proportional to the charge and inversely proportional to the distance r. The electric potential for an isolated point charge is V=kQ/r, where V is the electric potential in volts, Q is the charge of the particle, r is the distance from the point charge, and k (9x109 N m2 C-2 ) is a constant derived from Coulomb's law. The electric potential of a system of two or more charges can be obtained by applying the superposition principle. The superposition principle states that the total potential at some point P due to several point charges is the algebraic sum of the potentials due to the individual charges. So for a system of two charges the potential at point P is V=k(q/r+q/r), where q is the charge of particle 1 that is a distance r from point P, and q is the charge of particle 2 that is a distance r from point P.
The difference in electric potential between two points is referred to as the voltage or electromotive force. It is not actually a force but a difference in potential that is capable of doing work. The actual force is dependent upon the charge and distance involved.
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