An electric field is a field that surrounds a stationary electric charge or changing magnetic field and exerts a force on charged objects. The electric field or electric field intensity is a vector quantity, and the electric field strength is the magnitude of this vector. Electric field is defined as the electric force per unit charge. The direction of the field is taken to be the direction of the force it would exert on a positive test charge. The electric field is radially outward from a positive charge and radially in toward a negative point charge.

The strength of the field upon a unit charge at a distance r from a charge Q is equal to Q/4πr ²ε, where ε is the permittivity of the medium surrounding the charge.