Gauss’ Law: Help for the Problems

• How to do practically all of the homework problems

RHS: q = ALL charge inside radius r

RHS: q = ALL charge inside radius r, length L

RHS: q = ALL charge inside cylinder=sA

http://wug.physics.uiuc.edu/courses/phys112/fall97/acts/lect04/act04c/sld001.htm

• Gauss’ Law is ALWAYS VALID!!

• What Can You Do With This??
  If you have (a) spherical, (b) cylindrical, or (c) planar symmetry AND:
  
  • If you know the charge (RHS), you can calculate the electric field (LHS)
  • If you know the field (LHS, usually because E=0 inside conductor), you can calculate the charge (RHS).

• Spherical Symmetry: Gaussian surface = Sphere of radius r

• Cylindrical Symmetry: Gaussian surface = Cylinder of radius r

• Planar Symmetry: Gaussian surface = Cylinder of area A

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