Electric Field. Electric fiel d lines: Start on positive charges; end on negative charges Follow the direction taken by a positive test charge Never cross The density of field lines show the strength of the electric field.
Electric field lines:
How many things are incorrect with the electric field line pattern shown below?
Consider the two plates mounted on insulators so that the charge on each plate is constant
The electric field is uniform and depends only on the plate charge! ( q)
If the plate separation changes then is NOT affected!
Note: This does not hold if the plates are attached to a battery. As the plate separation changes, the battery works to maintain constant voltage and the plate charge changes.
Electric Field and Shielding
Sensitive electrical components are shielded from the effects of external electric fields by placing them in metal boxes(Faraday Cage)
The external field will NOT produce a field inside the box!!
Isolated Conductor in an Electric Field
Charges in the conductor distribute themselves on surface until they are in equlibrium
Electric field is perpendicular to the surface of the conductor (so charges won’t move on the surface!)
= 0 inside!!