1. Apply Gauss’s law 2. Choose Gaussian surface so that E can be taken out of integration: explore the symmetry of E Symmetry of EGaussian Surface Spherical (point & spherical charges)Sphere Cylindrical (line charge)Cylinder Planar (sheet of charge)Box or cylinder E are the same everywhere on surface (sphere), often  =0 or 180 so that cos0=1 or cos180=-1 E  surface (align on the surface): cos90=0 Combination (cylinder) 1. Point of interest has to be on Gaussian surface

2. Apply Gauss’s law 3. Add all charges inside Gaussian Surface: algebraic sum  1 <0  2 >0 +q outside 4. Calculate E.

3. Concept Check: Gauss’ law +q p p -q +q p A B C Which situation has more electric flux through the closed surface? Which situation has the largest E at the point P?

4. Gauss’ Law: Examples One last reminder: superposition principle is still valid! Examples: parallel plates (better consider it as a thin sheet) Concentric cylindrical rod and shell (electric cable) Spheres with uniform charge distribution (insulating)