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electrostatic field[i‚lek·trə′stad·ik ′fēld]
an electric field that consists of stationary electric charges interacting with each other. Like a variable electric field, an electrostatic field may be characterized by electric field strength E, which is the ratio of the force acting on a charge to the magnitude of the charge. The lines of force, which determine the field strength, are not closed: they extend from positive charges to negative charges. In dielectrics, the electrostatic field is characterized by the vector D, known as electric flux density (seeINDUCTION, ELECTRICAL AND MAGNETIC), which satisfies Gauss’ theorem.
An electrostatic field is a potential field; that is, the work of the field in moving an electric charge between two points does not depend on the shape of the trajectory. Over a closed path, the work is equal to zero. Owing to its potential character, an electrostatic field can be represented by a single scalar function—the electrostatic potential φ, which is related to the vector E by the equation E = – grad φ. The potential φ satisfies Poisson’s equation.
In a homogeneous dielectric, the electrostatic field is decreased by a factor oft, where e is the permittivity. The electrostatic field inside a conductor is equal to zero, whereas all points on the conductor’s surface have the same potential φ. If there is a cavity in the conductor, the electrostatic field in the cavity is also equal to zero. Electrostatic shielding is based on the latter phenomenon.