Electric ChargeO All ordinary matter

contains both positive and negative charge.

O You do not usually notice the charge because most matter contains the exact same number of positive and negative charges.

O An object is electrically neutral when it has equal amounts of both types of charge.

Electric ChargeO Objects can lose or gain electric

charges.O The net charge is also

sometimes called excess charge because a charged object has an excess of either positive or negative charges.

O A tiny imbalance in either positive or negative charge on an object is the cause of static electricity.

Electric ChargeO Electric charge is a

property of tiny particles in atoms.

O The unit of electric charge is the coulomb (C).

O A quantity of charge should always be identified with a positive or a negative sign.

Electric ForcesO Electric forces are created between all electric

charges. O Because there are two kinds of charge

(positive and negative) the electrical force between charges can attract or repel.

Electric ForcesO The forces between the two kinds of charge can

be observed with an electroscope.

Electric ForcesO Charge can be transferred by conduction.

Electric Current

O Current is the movement of electric charge through a substance.

Current (amps)

Charge that flows

(coulombs)

Time (sec)

I = q t

Calculate Current

O Two coulombs of charge pass through a wire in five seconds.

O Calculate the current in the wire.

Coulomb's LawO Coulomb’s law relates the force between two

single charges separated by a distance.

Force (N)

Constant9 x109 N.m2/C2

Distance (m)

F = K q1 q2

r2

Charges (C)

Coulomb's Law

O The force between two charges gets stronger as the charges move closer together.

O The force also gets stronger if the amount of charge becomes larger.

Coulomb's Law

O The force between two charges is directed along the line connecting their centers.

O Electric forces always occur in pairs according to Newton’s third law, like all forces.

Coulomb's LawO The force between charges

is directly proportional to the magnitude, or amount, of each charge.

O Doubling one charge doubles the force.

O Doubling both charges quadruples the force.

Coulomb's LawO The force between charges

is inversely proportional to the square of the distance between them.

O Doubling the distance reduces the force by a factor of 22 = (4), decreasing the force to one-fourth its original value (1/4).

O This relationship is called an inverse square law because force and distance follow an inverse square relationship.

Calculating Force

O Two balls are each given a static electric charge of one ten-thousandth (0.0001) of a coulomb.

O Calculate the force between the charges when they are separated by one-tenth (0.1) of a meter.

O Compare the force with the weight of an average 70 kg person.

Fields and ForcesO The concept of a field is used to describe any

quantity that has a value for all points in space.O You can think of the field as the way forces are

transmitted between objects.O Charge creates an electric field that creates

forces on other charges.

Fields and ForcesO Mass creates a gravitational field that exerts

forces on other masses.

Fields and ForcesO Gravitational forces are far weaker than electric

forces.

Drawing the Electric Field

Electric Fields and Electric Force

O On the Earth’s surface, the gravitational field creates 9.8 N of force on each kilogram of mass.

O With gravity, the strength of the field is in Newton per kilogram (N/kg) because the field describes the amount of force per kilogram of mass.

Electric Fields and Electric Force

O With the electric field, the strength is in Newton per coulomb (N/C).

O The electric field describes the amount of force per coulomb of charge.