It polarizes dielectrics, allowing capacitors to store energy in capacitors.  
In semiconductors, the mobility is multiplied by this entity to get drift velocity. In the Lorentz force law, unlike a similar quantity it is not multiplied by the velocity. Its divergence is equal to the charge density divided by the permittivity of space. The cross product of this quantity with the magnetic field appears in the equation for the Poynting Vector. The Stark effect refers to this entity splitting spectral lines. It polarizes dielectrics, allowing capacitors to store energy in capacitors.  For 10 points, name this field whose magnitude at a location is defined as the strength of the force divided by the point charge that experienced it.
In semiconductors, the mobility is multiplied by this entity to get drift velocity.
electric field