Seven Chapter 3

Electric Fields Inside And Around A Conductor

• When like charges are placed on a conductor, they repel and move as far apart as possible. Therefore:
  • Any charge placed on an insulated conductor resides entirely on the outer surface.
  • The electric field inside the conductor insulated from its surroundings is zero.
• Consequences
  • The electric field is perpendicular to the surface of the conductor where the charges are in static equilibrium (no forces on them) and the conductor is symmetrical.
  • If the conductor is asymmetrical, the charges will concentrate at pointed ends and therefore electric fields are greater there.
    • At these points, F_e on the charges is greater and therefore a spark may form to discharge the conductor.
    • F_e inside the conductor is zero since E is zero.

• If the conductor is in an electric field, the field can alter the charge distribution on the surface, but the electric field inside still adds to zero.
• This concept is used for electrostatic shielding

E.g. Cable TV - the wire is wrapped in foil to shield it so external fields do not interfere with the signal

Electronic components are covered by metallic shields to prevent damage from external fields.

December 30, 2013