Charges in a Conductor

  • Charge is free to move until the E=0

    oo Negative e ectric charges are given inside a conductor. Coulomb
force (repulsive force) works for each charge. Distribution Of
electric charges on the charged conductive sphere. The e ectric
charges are distributed on the conductor surface and there is no
electric charge inside the conductor.

  • All charge resides at surface


  • Field lines are perpendicular to the surface

    Field weakest E = D inside Field strongest (d) Electric field &
charge distribution around a pear-shaped conductor

Electric Field at the Surface of a Conductor

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  • E increases as r σ increases.

Hollow Conductors

Hollow conductor (a) (b) (c) (d) Figure 24.20 An experiment showing
 that any charge trans- ferred to a conductor resides on its surface in
 electrostatic equilibrium. The hollow conductor is insulated from
 ground, and the small metal ball is supported by an insulating thread.

o o o O o o o o 9 o o o o Faraday Cage o Electrical Field The
 charged particles in the wall Of the Faraday cage respond to an
 applied electrical field. o o Metal wall o o o o o o o o o Faraday
 Cage in the absence Of an electrical field. Electrical fields
 generated inside the wall cancel out the applied field, neutralizing
 the interior of the cage.

Example 1: Conducting Spheres Connected by a Wire


  • Two conducting spheres, A and B, are placed a large distance from each other. The radius of Sphere A is 5 cm, and the radius of Sphere B is 20 cm. A charge Q of 200 nC is placed on Sphere A, while Sphere B is uncharged. The spheres are then connected by a wire. Calculate the charge on each sphere after the wire is connected

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2004 Free Response Question

Conductor E\&M. 1. r2 111 11 1 0+1 •d •a Conductor Cross Section The
 figure above left shows a hollow, infinite, cylindrical, uncharged
 conducting shell of inner radius rl and outer radius r2 . An infinite
 line charge of linear charge density +1 is parallel to its axis but
 off center. An enlarged cross section of the cylindrical shell is
 shown above right. (a) On the cross section above right, i. sketch the
 electric field lines, if any, in each of regions I, Il, and Ill and
 ii. use + and — signs to indicate any charge induced on the conductor.
 (b) In the spaces below, rank the electric potentials at points a, b,
 c, d, and e from highest to lowest (1 = highest potential). If two
 points are at the same potential, give them the same number.


Nonconductor Nonconductor Cross Section (c) The shell is replaced by
 another cylindrical shell that has the same dimensions but is
 nonconducting and carries a uniform volume charge density +P . The
 infinite line charge, still of charge density +1 , is located at the
 center of the shell as shown above. Using Gauss's law, calculate the
 magnitude of the electric field as a function of the distance r from
 the center of the shell for each of the following regions. Express
 your answers in terms of the given quantities and fundamental


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