1. Chapter 28
Gauss’s Law
28.1 to 28.4

2. Symmetry
An object is symmetric if a group of geometrical transformations don’t cause any physical change.
Translate, rotate, and reflect

3. Cylindrically and Spherically Symmetric
The symmetry of the electric field must match the symmetry of the charge distribution.
Cylindrically symmetric charge distribution cannot have a component parallel to the cylinder axis.
It cannot have a component tangent to the circular cross section.

4. Three types of Symmetries

5. Gaussian Surface
Definition: A closed surface that divides space into distinct inside and outside regions.
The electric field must be perpendicular to the surface
Same Magnitude at each point
Appropriate Gaussian Surface
Inappropriate Gaussian Surface

6. Types of Flux
If the net amount of flux lines go out of Gaussian surface, then positive charge inside.
If the net amount of flux lines go into a Gaussian surface, then negative charge inside
If the net amount of flux lines is equal to zero, then no charge inside.
Page 855, Stop-to Think 27.2

7. Calculating Electric Flux

8. Electric Flux through a Closed Surface
Closed surface completely surrounds a region.
If the electric field is everywhere tangent to a surface, the electric flux through the surface is Fe=0
If the electric field is everywhere perpendicular to a surface and has the same magnitude E at every point, the electric flux through the surface is Fe=EA
Try Stop to Think 27.3
Examples

9. Gauss’s Law

10. Determine Electric Field Equation for a point charge from Gauss’s Law

11. Practice Problems
Stop to Think 28.1 to 28.4
Page 875, #6, 8,17,20,23