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Flashcards in Chapter 20 Deck (22):
1

Potential energy, U

-depends only on position (U=mgy)
-change in U is independent of path

2

Total energy is:

-Eini=Kini+Uini
-conserved

3

Work

W=-deltaU
-units: volts, or J/C

4

Motion of charges particles in electric fields

Just like a particle moving near the earth surface for a constant field

5

Electric potential energy

-total energy is conserved

6

Electric potential

The potential difference between that pint and a reference point

7

Potential from N charges

The algebraic sum of the potential due to each charge separately

8

Equipotentials

-the locus points with the same potential
-electric field is always perpendicular to an equipotential surface
-along the surface there is not change in V, therefore no component along surface

9

Conductors

-the surface of a conductor is always an equipotential surface
-if surface were not equipotential, there would be an electric field component parallel to the surface and the charges would move

10

How is charge distributed on the surface of a conductor?

-must produce E=0 inside the conductor and E normal to the surface

11

Equipotentials and conductors

-field lines more closely spaced near end with most curvature
-field lines perpendicular to surface near the surface
-equipotentials have similar shape as surface near the surface
-equipotentials will look more circular at a large r

12

Equipotential surfaces and electric field

-an ideal conductor is an equipotential surface
-if two conductors are at the same potential, the one that is more curved will have a larger electric field around it
-this is also true for different parts of the same conductor

13

Capacitor

A device whose purpose is to store electrical energy which can then be released in a controlled manner; consists of two spatially separated conductors which can be charged to +Q and -Q respectively

14

Capacitance

-derived from the capacity to carry a charge Q when a voltage V is applied
-defined as the ratio of the charge on one conductor of the capacitor to the potential difference between the conductors

15

A capacitance C of the device...

-should not depend on Q or V
-should depend on how it is made (material, geometry, dimensions)
-should be intrinsic to the capacitor

16

Parallel plate capacitor

Capacitance depends only on its geometry

17

Dimensions of capacitance

The Farad; C/V

18

Dielectrics

Inserting a non-conducting material between the plates of a capacitor changes the value of the capacitance, lowers the potential difference, and increases the capacitance

19

Definition: dielectrics

An insulating material that, when placed between the plates of a capacitor, increases the capacitance due to polarization of the material

20

Dielectric constant

The ratio of the capacitance when filled with the dielectric to that without it

21

Dielectric breakdown

If the electric field in a dielectric becomes too large, it can tear the electrons off the atoms, thereby enabling the material to conduct; occurs at dielectric strength

22

Where is energy stored?

Energy is stored in the electric field itself. The energy needed to charge the capacitor is the energy needed to create the field