University:
Kentucky State University
Course:
PHY 212 | General Physics II
Academic year:

2019
Views:

251

Pages:

9
Author:

Caroline Mcfarland

Conductors in Electrostatic Equilibrium Free electron (Copper) Vs Bound electron (Rubber) Electrostatic equilibrium means there is no net motion of the charges inside the conductor. 1) The electric field inside the conductor must be zero. If this were not the case, charges would accelerate. 2) Any excess charge must reside on the outside surface of the conductor. No net charge on the interior surface of the conductor. Apply Gauss’ law to a Gaussian surface just inside the conductor surface. The electric field is zero, so the net charge inside the Gaussian surface is zero. Any excess charge must go outside the Gaussian surface, and on the conductor surface. 3) The electric field just outside a charged conductor must be perpendicular to the conductor’s surface. Otherwise, the component of the electric field parallel to the surface would cause charges to accelerate. 4) The magnitude of the electric field just outside a charged conductor is equal to /0, where  is the magnitude of the local surface charge density. Example: a conducting spherical shell of inner radius a and outer radius b with a net charge -Q is centered on point charge +2Q. Use Gauss’s law to show that there is a charge of -2Q on the inner surface of the shell, and a charge of +Q on the outer surface of the shell.   q enclosed  E  dA  ε 0 -Q r a E=0 inside the conductor! +2Q b QI q enclosed QI  2Q 0   QI  -2Q ε0 ε0 Example: a conducting spherical shell of inner radius a and outer radius b with a net charge -Q is centered on point charge +2Q. Use Gauss’s law to show that there is a charge of -2Q on the inner surface of the shell, and a charge of +Q on the outer surface of the shell. QI  -2Q -Q r From Gauss’ Law we know that excess charge on a conductor lies on surfaces. a +2Q b QI Electric charge is conserved: Qshell  -Q  Q I  QO  -2Q Q O QO - Q  -2Q  QO  Q O  Q