#ph504

[physicsandchemistryrevision]

Electromagnetism & Optics

Electrostatics Electric fields See "Coulombs law" and "Principle of superposition" 

Electric fields are a byproduct of Coulombs law and the principle of superposition. By equating the two we can see that

F = Σ 1/4πε0 · qiQ/|ri|² · ri = Σ Fi

and so

F(r) = Q · [ 1/4πε0 Σ qi/|ri|² · ri ]

If we define the electric field vector E to be

E(r) ≡ 1/4πε0 · Σ qi/|ri|² · ri 

then

F = QE

As we can see, the electric field is a function of position r within the field but is independent of the test charge Q.