Chapter 28 Gauss’s Law 28.1 to 28.4

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

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.

Three types of Symmetries

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

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

Calculating Electric Flux

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

Gauss’s Law

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

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