Electric Chargeand

Electric Field

Write at least three questions that you have about ELECTRICITY.

QuestionsWhat causes electricity?Why is electricity harmful? How much is

lethal?What is the difference between static

electricity and current electricity?What makes electrons move?What is the difference between an amp and

a volt?What makes a conductor conductive?

Questions1. T or F, Electric charges behave just like

magnets in that they only repel each other.

VocabularyElectrostatics

Electric Charge

Neutral

Insulator

Conductor

Charging by induction

Law of conservation of charge

Coulomb’s law

Elementary charge

Electrons

Permittivity of free space

Principle of superposition

Electric field

ReadingChapter 16, Electric Charge and Electric Fields

Electrostatics

Study of electrical charges collected and held in one place

Examples

Static electricity from the clothes dryer

Static electricity from combing your hair

Where does charge come from?

Conductors and Insulators

Elementary ChargeOne electron has a charge of

1.602 x 10 -19 Coulombs

One coulomb is the charge on 6.25 x 10^18 electrons

A large lightning bolt is about 10 coulombs

Conservation of Charge

CHARGE

Can be transferred

Cannot be created or destroyed

Electric ChargeLike charges repel. Opposite charges attract.

Separation of ChargeAn electroscope can be used to detect the presence and relative amount.

Charging by Induction

Coulomb’s Law

Click image to view movie.

Coulomb’s Law•Used to calculate the magnitude of electric force•Inverse square law

Similarities Between Coulomb’s Law and Newton’sLaw of Universal Gravitation

Inverse Square Laws

Forces on Charges

Coulomb’s LawTwo balloon’s are located 15 cm apart. Each

balloon holds a charge of +6.0 μC.

Calculate the electrostatic force is exerted by each balloon.

Superposition of Forces- Find force on charge A

Example Problem: Determining the Total Force Exerted on the Positive Charge

Electric FieldsHow can you tell that Earth has a

Gravitational Field?

Electric Fielda region around a charged object where the object’s electric

force is exerted on other charged objects.

Electric Field• The strength of an electric field is equal to the

force on a positive test charge divided by the strength of the test charge.

• The direction of an electric field is the direction of the force on a positive test charge.

• A test charge always must be small enough so that its effect on “Q” is negligible.

• The magnitude of the electric field strength is measured in Newtons per coulomb, N/C.

Example Problem- Electric FieldA positive test charge of 3.0 x 10-6 C experiences a force of

0.12 N at an angle of 15º north of east. What are the magnitude and direction of the electric field at the location of the test charge.

Drawing Electric FieldsAn electric field is a region around a charged object where the object’s electric force is exerted on other charged objects.

Electric Fields

Additional Resources

Use Electricity and Magnetism CD

Use www.falstad.com

Quiz- Draw the Electric Field1. A positive charge

2. A negative charge

3. One positive and one negative charge of equal magnitude

4. Two positive charges of equal magnitude

5. Two negative charges of equal magnitude

6. One positive and one negative charge of unequal magnitude

7. Two positive charges of unequal magnitude

8. Two parallel plates with opposite charges

Superposition of E-fields

E = E1 + E2 + E3

E = F/q = F1/q +F2/q +F3/q

Van de Graaff Generator

HomeworkPhysics: Principles and Problems, Glencoe

Electric Charge

Chapter 20, p558-559, #23-28, 30, 34-36, 41-43, 49, 51

Electric Field

Chapter 21, p.585-587, #67, 71, 73, 74

AP Physics

Additional Slides

JJ Thompson’s Experiment

Rutherford’s Gold Foil Experiment

Transferring Charge

There are three methods by which charges can be transferred to build up static electricity: charging by friction, by conduction, and by induction.

Electric ForceAn electric field is a region around a charged object where the object’s electric force is exerted on other charged objects.

Lightning

Click the Video button to watch a movie about lightning.

Electric ForceAn electric field is a region around a charged object where the object’s electric force is exerted on other charged objects.