Educator

Electric Field

• Electric charges produce an electric field that fills the space. To find the value of the electric field E at a point, we place a very small point charge q at that point and measure the force F acting on the point charge; the electric field is then given by E = F / q. Note that the electric field is a vector, since F is a vector.
• The electric field produced by a point charge Q at a distance r has a magnitude E = kQ/r^2. The field is directed radially outward if Q is positive and radially inward if Q is negative.
• The electric field produced by a collection of point charges is equal to the vector sum of the fields produced by the individual point charges.
• Between the plates of a charged parallel-plate capacitor, E = σ / ε0, where σ is the surface charge density on the plates and ε0 is the permittivity of free space.
• Electric field lines are always tangent to the electric field at every point in space. The lines always begin at positive charge and end on negative charge, and their density is proportional to the field strength.
• Under electrostatic conditions, any excess charge, added to a conductor, must reside on the conductor surface.