1. Quizzes 3 A cube with 1.40 m edges is oriented as shown in the figure
Suppose the cube sits in a uniform electric field of 10i ?
What is the magnitude of the flux through the whole cube?
What is the magnitude of the flux through the top side?
How many sides have nonzero flux?
q/eo D) q/6eo
q/4eo
2 D) 1 4

2. Applying Gauss’s Law
Can be used to determine total flux through a surface in simple cases
Must have a great deal of symmetry to use easily
charge q
Charge in a long triangular channel
What is flux out of one side?

3. Applying Gauss’s Law L R r
Draw a cylinder with the desired radius inside the cylindrical charge
Infinite cylinder radius R charge density 
What is the electric field inside and outside the cylinder?
Electric Field will point directly out from the axis
No flux through end surfaces

4. Applying Gauss’s Law L R r
Draw a cylinder with the desired radius outside the cylindrical charge R
Infinite cylinder radius R charge density 
What is the electric field inside and outside the cylinder?
Electric Field will point directly out from the center
No flux through endcaps

5. Applying Gauss’s Law Sphere volume: V = 4a3/3 R Sphere area: A = 4a2
Draw a Gaussian surface inside the sphere of radius r r R
Sphere radius R charge density . What is E-field inside?
What is the magnitude of the electric field inside the sphere at radius r?
R3/30r2
r2/30R
C) R/30 D) r/30

6. Conductors in Equilbirum
A conductor has charges that can move freely
In equilibrium the charges are not moving
Therefore, there are no electric fields in a conductor in equilibrium
= 0
= 0
The interior of a conductor never has any charge in it
Charge on a conductor is always on the surface

7. Electric Fields near Conductors
No electric field inside the conductor
Electric field outside cannot be tangential – must be perpendicular
Area A
Add a gaussian pillbox that penetrates the surface
Surface charge 
Electric field points directly out from (or in to) conductor

8. Conductors shield charges
Draw a Gaussian surface
No electric field – no charge
Inner charge is hidden – except
No net charge
Charge -q
What is electric field outside the spherical conductor?
Charge +q
Charge q
Charge +q on outside to compensate
Charge distributed uniformly