Electrostatics Ch 32 & 33. Basic Concept In Mechanics, the basic property of matter is Mass. In Electricity, the basic property is Charge.

ElectrostaticsCh 32 & 33

Basic Concept

In Mechanics, the basic property of matter is Mass.

In Electricity, the basic property is Charge.

Basic Units

Compare Smallest Possible Unit

Practical Unit

US Currency Penny$0.01 = 1/100th of a dollar

Dollar$1 = 100 Pennies

Electric

Charge

Elementary Charge (1e)electron or proton

1e = 1.6 x 10-19C

Coulomb1C = 6.25 x 1018e

Examples

How many electrons are on a conductor if it has a charge of -4 x 10-17 C?250 electrons

What charge will 120 protons have?1.92 x 10-17 C

Example

Why is it not possible for any object to have a charge of 8 x 10-20 C?

Electrons (or protons) cannot be broken down into smaller pieces.

Movement of Charge

ConductorsElectrons are free to moveMost metals

InsulatorsElectrons are not free to move

Basic Concept

Opposite Charges Attract

Like Charges Repel

+

-

+

-

-

+

Movement of Charge

GroundingCharges on an object will try to move away

from like charges or towards opposite charges

ExamplesLightning, Static electricity

Charging by Contact

When 2 conductors of unequal charges touch, the electrons will move to balance out the charge, leaving both conductors with the same charge

Charging by Induction

If a charged object is brought near a conducting surface, even without physical contact, electrons will move in the conducting surface. Read 32.6

Charging by Induction

Review

Gravitational Force

What factors affect gravitational force? Size of each mass Distance of separation

221

r

mGmFg

Electrostatic Force

What factors will affect the amount of attraction or repulsion?Size of each chargeDistance of separation

Coulomb’s Law

k = Electrostatic constant, 8.99 x 109 Nm2/C2

q = charge (C) r = distance separating the center of each

charge (m)

Fkq q

rE 1 22

Electric Fields

Electric Field is a region around a charged object through which a force is exerted on any other charged particle.

Electric Field Lines are imaginary lines drawn to show electric field

Electric Field Lines

Lines are not real Positive Negative Can not cross Closer lines mean stronger field

+ -

Electric Fields

Parallel Plates Electric Field is uniform between plates

+ + + + + + + + + + + + +

- - - - - - - - - - - - - - - - - -

Electric Field Strength, E

Force per charge Amount of force felt

by a charge Vector

E (N/C) Fe (N)

q (C)

EF

qe