demos

• Intro: electricity is gonna be big

Ac/Hon Physics Notes

Chapter 20Electostatics

Lesson 1Definitions and concepts

Objectives

• At the end of this lesson you will be able to:– Define electric charge and explain how forces act

between charged objects

Electricity!

• Electricity: – Flow of electrons

• Electrostatics– Study of electrons

(and protons) standing still

The Atom and Electric Charges

• Electrons– Negative charge

• Protons– Positive charge

Electrostatic Force

• Like charges repel each other• Unlike charges attract each other• The attraction or repulsion is called:– Electrostatic Force

• It is a force like all other forces we’ve studied in this class– Units = ??– Newtons

Electrostatic Force vs. Gravity

Electrostatic Force Gravitational Force

Field force Field force

Force due to electric charge Force due to mass

Can repel or attract Can only attract

Other fun facts

• All Electrons and protons are the same regardless of what kind of atom

Questions

• What is electric charge?• What causes electrostatic force?• Why do like charges repel and vice versa?– Electrostatic Force

Stop asking so many questions.We have no idea.Just accept it

How do we measure electric charge?• Coulombs (C)– Charles-Augustin de Coulomb (1736-1806)

• Charge of an electron or protone = 1.602 × 10-19 C+ for proton- for electron

• How do we get more charge (more Coulombs)?

• Add more electrons or protons• Wait – do we ever add protons?

We’ll get to this later….

What is the electrical charge of an atom?

• Zero• It has the same # of protons and electrons• Zero charge Charge Neutral

How do we give something a charge?

• Add or take away electrons– Protons don’t move

• Adding electrons– Gives negative charge

• Removing electrons– Gives positive charge

• Atoms with a missing OR extra electron are called:– Ions

Conductors and Insulators

• Conductors– Electrons move easily through

• Insulators– Electrons stay put

Charge Conservation

• Electrical charge can never be created or destroyed

• It only moves

Lesson 2Charging objects

Objectives

• At the end of this lesson you will be able to:– Solve problems involving moving of charge

Lesson 2Charging objects

Objectives

• At the end of this lesson you will be able to:– Solve problems involving moving of charge

Ways things get charged

• Conduction– 2 things touch and electrons move

• Induction– 2 things come close to each other and electrons

get pushed or pulled – we’ll explain this more soon…

What electrons like to do

• If there is no force on them, electrons spread out evenly

What’s up with “Ground”

• Earth is big• It has a lot of electrons – really a lot• If a charged object comes in contact with the

earth, it automatically becomes neutral• We say this object has been “grounded”• Explain why…

Charging Problems

• Do on board– A charged object comes in contact with a charge

neutral object (pos and neg)– A charged object come near a charge neutral

object that’s grounded and the ground is removed.

Why will a charged object attract a charge neutral object like in the paper

and ruler demo• Do on board

Electorsopes

• A tool that tells you when it is charged.• Do on board

Lesson 3Coulomb’s Law

Objectives

• At the end of this lesson you will be able to:– Apply Coulomb’s Law

Coulomb’s Law

• Tells us how big the force is between 2 charged objects (let’s call them A and B

• Where F is the force (same on and B but opposite directions)

• K = 9.0 x 109 Nm2/C2

• qa and qb are the charges of A and B respectively

• r is the distance between the charges