# Electric field

In physics, an electric field or E-field is an effect produced by an electric charge that exerts a force on charged objects in its vicinity. The units of the electric field are newtons per coulomb or volts per meter (both are equivalent). Electric fields are composed of photons and contain electrical energy with energy density proportional to the square of the field intensity. In the static case, an electric field is composed of virtual photons being exchanged by the charged particle(s) creating the field. In the dynamic case the electric field is accompanied by a magnetic field, by a flow of energy, and by real photons.

## Properties

According to Equation (1) above, electric field is dependent on position. The electric field due to any single charge falls off as the square of the distance from that charge.

Electric fields follow the superposition principle. If more than one charge is present, the total electric field at any point is equal to the vector sum of the respective electric fields that each object would create in the absence of the others.

[itex]E_{tot} = E_1 + E_2 + E_3 \ldots \,\![itex]

If this principle is extended to an infinite number of infinitesimally small elements of charge, the following formula results:

[itex]

\mathbf{E} = \frac{1}{4\pi\epsilon_0} \int\frac{\rho}{r^2} \mathbf{\hat r}\,d^{3}\mathbf{r} [itex]

where ρ is the charge density, or the amount of charge per unit volume.

The electric field is equal to minus the gradient of the electric potential. If several spatially distributed charges generate such an electric potential, e.g. in a solid, an electric field gradient may be defined.

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