January 14, 2005 Electrostatics 1

Lecture 1-3Charge Completed

January 14, 2005

January 14, 2005 Electrostatics 2

Whatsup? Short Quiz Today Complete the topic of Charge

There is a WebAssign for this chapter.

Chapter 21 should have been read.

Next Week Monday = MLK Holiday Wed, Fri – the Electric Field (Ch-

22)

January 14, 2005 Electrostatics 3

January 14, 2005 Electrostatics 4

Quick Review

When objects are rubbed together or pulled apart, the two surfaces are found to be CHARGED.

Two kinds of Charge – Positive (The rubber rod after dead

cat) Negative (The glass rod after being

rubbed with wool or silk.)

January 14, 2005 Electrostatics 5

Charge can be TRANSFERRED OR SEPARATED

Contact Induction (With some

“Grounding”)

Polarization

January 14, 2005 Electrostatics 6

That Balloon …

Sorry – ours wasyellow.

January 14, 2005 Electrostatics 7

Another Experiment

??

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Charged Rod

InitiallyNeutralMetal

Sphere

January 14, 2005 Electrostatics 8

Types of Materials

Insulators negative charges can move only

with great difficulty Metal

negative charges move quite easily. Semiconductor

Ability for the negative charge to move depends on the impurities in the material as well as the temperature.

Semi-Metals Don’t ask!

January 14, 2005 Electrostatics 9

What is this “charge” thing?

There are two charged particles we will be concerned with: Electrons Protons

Electrons have a charge of –e Protons have a charge of +e ALL charges are an integral

multiple of this fundamental charge “e”

January 14, 2005 Electrostatics 10

The Atom

LIGHT

January 14, 2005 Electrostatics 11

What is e??

|e|=1.6 x 10-19 Coulombs

Exact value in textbook

January 14, 2005 Electrostatics 12

How Do We Know???Millikan Oil Drop Experiment

A Critical Balance

January 14, 2005 Electrostatics 13

The Electroscope& Induction Again

January 14, 2005 Electrostatics 14

January 14, 2005 Electrostatics 15

electrons

January 14, 2005 Electrostatics 16

Let’s Work a Few Problems if we

have time.

January 14, 2005 Electrostatics 17

In the figure, particle 1 of charge +1.0 µC and particle 2 of charge -4.0 µC, are held at separation L = 11.0 cm on an x axis. If particle 3 of unknown charge q3 is to be located such that the net electrostatic force on it from particles 1 and 2 is zero, what must be the coordinates of particle 3? x=[-11] cm y=[0] cm

January 14, 2005 Electrostatics 18

January 14, 2005 Electrostatics 19

Let’s Try It!

January 14, 2005 Electrostatics 20

A mechanics problem from the past!

January 14, 2005 Electrostatics 21

Free Body Forces?

January 14, 2005 Electrostatics 22

January 14, 2005 Electrostatics 23

Find force on lower left Find force on lower left particle.particle.