10.4: Electric Fields

A Describe the electric field produced by a charged object or configuration of point charges.

Electric fields may originate from monopole sources.

The electric field at a given point is the ratio of the electric force exerted on a test charge at that point to charge of the test charge.

• A test charge is a point charge with a small enough charge such that its presence does not significantly affect the electric field in its vicinity.

• The electric field points away from isolated positive charges and toward isolated negative charges.

• The electric force exerted on a positive test charge by an electric field is in the same direction as the electric field. The electric force exerted on a negative test charge by an electric field is in the opposite direction of the electric field.

Electric field is a vector quantity and can be represented in space using vector field maps.

• The net electric field at a given location is the vector sum of individual electric fields created by nearby charged objects.

• Electric field maps use vectors to depict the magnitude and direction of the electric field at many locations within a given region.

• Electric field line diagrams are simplified models of electric field maps and can be used to determine the relative magnitude and direction of the electric field at any position in the diagram

Describe the electric field generated by charged conductors or uniformly charged solid objects

While in electrostatic equilibrium, the excess charge of a solid conductor is distributed on the surface of the conductor, and the electric field within the conductor is zero.

• At the surface of a charged conductor, the electric field generated by the conductor is perpendicular to the surface.

• When determining the electric field generated by an isolated charged conducting sphere at positions outside the sphere, the sphere can be treated as a point charge located at the center of the sphere.

While in electrostatic equilibrium, the excess charge of an insulator is distributed throughout the interior of the insulator as well as at the surface, and the electric field within the insulator may have a nonzero value.