where E = F/q0


A vector field is a rule that assigns a vector to every point in space. Faraday invented the electric and magnetic fields, E and B, so that he could solve problems in electricity and magnetism by drawing pictures.

Calculating E by direct integration of dE over a charge distribution is difficult because dE sweeps around as you integrate over dq. Thus it is important to make use of symmetry ideas as much as possible.


Click on the image to see a quick derivation of E for an infinite line of charge.






Note that the E field above an infinite sheet of charge, of charge surface density σ, has magnitude E = σ/(2ε0). In other words, it is the same at all points in space.   We will show this another way in the next chapter.  Therefore, between two parallel, oppositely charged plates, we get:



E field lines begin on + charges and end on − charges. If not enough charges exist to terminate a field line, it extends to infinity.

Because the charged hairs repel they align with the electric field, and so become living examples of E field lines!














Why does all dumped charge stay only on the surface of conductors? Why can external E fields not penetrate into a conductor? Why is the field at the surface of a conductor always precisely perpendicular to the surface?  We'll find out more in the next chapter.


A conductor in a uniform electric field E



What's wrong with this picture?!?!







A sad example of being “unclear on the concept” of what an in-class clicker quiz should be like.

Next
Back