E8 problems due at 8:00 today'

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• E8 problems due at 800 today.
• Our goal is to have a test over remaining
  electricity chapters the Friday before spring
  break.
• The general test over electricity and magnetism
  will be the first week after spring break
• This week Ch 10, 11, (12-skip)13, 14(?)
• We are going into less mathematical detail in
  these chapters, concentrate on the concepts.
• Next week 14, 15 test
• Next week begin a new 3 lab sequence (one day)
  and have a review Thursday.

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Chapter E10

• Gausss Law
• E10B.1, E10B.2, E10B.3, E10B.7,
• Due Wednesday

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Gausss Law
The product of the Electric Field and the area
vector is calculated over a closed surface.
The charge is that enclosed inside the surface.
The total flux through any enclosed surface is
the charge enclosed by that surface divided by
e0, where.
This is true of any surface, including imaginary
surfaces.
This is the first of 4 equations that taken
together completely describe all electricity and
magnetism.
4
Use Gausss law to prove that all excess charges
are on the surface of any conductor

• We know the electric field inside all conductors
  is zero
• If it is not zero, the electrons would move to
  make it zero.
• We choose our Gaussian surface to be just inside
  the surface of the conductor. As E0, the flux
  must be zero, so no change can be inside and all
  the charge must be outside.

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Using Gausss law to calculate electric fields.

• Use a symmetry that matches the charge
• Use a Gaussian surface that makes the calculation
  easy
• Calculate the flux
• Use Gausss law to calculate the field

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Calculating the field of a spherical charge
distribution.
Spherical charge distribution

• Note that the surface is
• At a place where E is constant
• At a place where E is perpendicular to the surface

Construct a Gaussian surface
7
Calculating the field of a cylindrical charge
distribution
Cylindrical charge distribution
Gaussian surface
Note that because E is parallel to the ends of
the cylinder, the flux through the ends is zero.
L
8
External field of an infinite slab
s0charge/m2
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Gausss law for a magnetic field
This equation shows us that in any closed surface
we choose, the same number of magnetic field
lines enter as leave the surface.
This is the second equation of the four equations.
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Problems for Wednesday

• E10B.1, E10B.2, E10B.3, E10B.7,