Exam 1

0

5

10

15

20

25

30

35

1 2 3 4 5 6 7

Series1

90 80 70 60 50 40

Average 78.4Median 84

Outline

• Applications of Gauss’s Law- The single Fixed Charge- Field of a sphere of charge- Field of a spherical shell- A Line of Charge• Conductors and Insulators• The electric field of a conductor• The field in the cavity of a conductor;

Faraday’s Cage

Gauss’s Law

The total flux of electric field out of any closed surface is equal to the charge contained inside the surface divided by .0

S

enclosedQSdE

0

A Charged, Thin Sheet of Insulating Material

++

+

+

++

+

++

++

02

E

Conductors and insulators

Charges reside at the surface of the conductor

Conductor

E=0+

+ ++

+

+++

++

+++

+

+

• There is no electric field inside a conductor• Net charge can only reside on the surface

of a conductor • Any external electric field lines are

perpendicular to the surface (there is no component of electric field that is tangent to the surface).

• The electric potential within a conductor is constant

2

1

120

r

r

rr SdEVV

since inside the conductor.0E

For any two points and inside the conductor 1r

2r

21 rr VV

The conductor’s surface is an equipotential.

Equipotential Surfaces

An equipotential surface is a surface on which the electric potential V is the same at every point.

Because potential energy does not change as a test charge moves over an equipotential surface, the electric field can do no work on such a charge. So, electric field must be perpendicular to the surface at every point so that the electric force is always perpendicular to the displacement of a charge moving on the surface.

Field lines and equipotential surfaces are always mutually perpendicular.

Eq

A field in a cavity of a conductorFaraday’s cage

Have a great day!