Electrostatics Ch 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 Coulomb 1C = 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 Conductors Insulators Electrons are free to move Most metals Insulators Electrons are not free to move

Basic Concept Opposite Charges Attract Like Charges Repel + - - - + +

Movement of Charge Grounding Examples Charges on an object will try to move away from like charges or towards opposite charges Examples Lightning, 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

Electrostatic Force What factors will affect the amount of attraction or repulsion? Size of each charge Distance 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)

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)