Semester 2:Unit 1

ElectrostaticsSpring 2015

Agenda 1/20/15

Welcome! Seating Chart Name Game Info Sheets

Introduction to Electrostatics Activity What do you know about this stuff?

Seating Chart

Arrange yourselves in alphabetical order ACROSS each ROW.

You have 2 minutes

GO!!

Agenda 1/21/15 Double Period

Collect Signed Syllabi

Complete Intro to Electrostatics Lab Think about: What causes charge? In what ways can charge build up?

Discuss findings from activity

Notes on types of charging

Begin Types of charging lab

HW: Complete analysis and conclusion of lab

Let’s talk

What are the parts of an atom? Which part moves most easily?

What is a conductor? Examples?

What is an insulator? Examples?

Big Question: What makes something a conductor or an

insulator?

Methods of Charging

Chapter 19

Conductors vs. Insulators

Conductor: allows charge flow easily

Metals

Insulator: doesn’t allow charge flow easily

Glass, dry wood, cloth, air,most plastics

Like Charges & Unlike Charges

Charge moves due to motion of electrons

Electrons are negatively charged

When two materials +, repel

When two materials -, repel

When one material + and one material -, attract

Charging by Conduction

Redistribution of charge by direct touching together of two objects

Made easier/quicker if both are electrical conductors

Originally uncharged material gets same charge concentration as originally charged material if contact between the two exists for a long period of time

Charging by Conduction

Charging by Friction

When two initially uncharged materials make contact, the better conductor grabs the electrons from the better insulator

In the process, both become charged

Substance w/more electrons becomes negative; other becomes positive

Charging by Friction

High affinity for electrons

(conductors)

Low affinity for electrons

(Insulators)

Charging by Induction

Charge accumulates on originally uncharged material due to a charged material being placed nearby the uncharged material at the same time as a ground is established.

Induction Example: Grounding

Induction Example: Contact

Induction Example: + Charge

Induction by PolarizationPolarized: the + and – charges are not evenly distributed in a material (+ pole and – pole)

When the charged material is an insulator (non-conducting), polarization occurs in the conductor and the two materials are attracted

Cellophane on plastic, balloon on shirt

Induction by Polarization

Agenda 1/22/15

Complete Types of Charging Lab At least 2 Problem Solving Activities Show off Physics Skills

Lab Exit Slip

Forces and Free Body Diagram Intro

HW: FBD Practice 1

Agenda 1/23/15 Physics Phriday

Discuss Types of Charging Analysis Turn in lab

Intro to Free Body Diagrams Practice

Coulomb’s Law Lab Netbook activity

HW: Complete Coulomb’s Law Lab Analysis

Before we start

On a separate sheet of paper:

Tell me the 4 types of charging

AND

Draw an example of each type

Agenda 1/26/15

Complete Coulomb’s Law Lab Graphing Hints Build Coulomb’s Law

Practice problems with C.L.

HW: Finish Write-Up for C.L. Lab

Graphing Hints

Indirect Relationship

F = -x

Inverse Square

F =1/x2Inverse Relationship

F = 1/x

F = x

Agenda 1/27/15

Discuss Coulomb’s Law Lab Determine the flaw in the program Complete Lab

Notes on Coulomb’s Law Practice Problems for CL

HW: Finish Write-Up for C.L. Lab

Coulomb’s Law

FE = k|q1||q2| / r2

k = Coulomb’s Constant = 9.0 x 109 Nm2/C2

q1 & q2: Charges in coulombs (C)

r = distance from center of one charge to center of the opposite charge (m)

If charges opposite, then attractive

If charges like, then repulsive force

Equal force upon both objects (Newton’s 3rd Law)

Opposites Attract, Likes Repel

Inverse Square Law

Like with sound intensity, there is an inverse-square relationship between force and distance of separation

Fundamental Charge

When an atom ionizes to +1 or -1 in chemistry, how much charge does this represent in coulombs?

+1 in chem = 1.60 x 10-19 C = e

1.60 x 10-19 C is smallest quantified charge

Proton = 1.60 x 10-19C, electron = -1.60 x 10-19C

Also called elementary charge

Net Charge

The net charge equals the (number of extra or deficient electrons) x ( +/- 1.60 x 10-19 C)

q = Ne

If you have a substance with 5 extra electrons, then q = (5) (-1.6 x 10-19 C)

= -8.0 x 10-19 C

Net Charge

What is the net charge in Coulombs of a... Fe atom?

Fe2+ ion?

Fe3+ ion?

Charge amounts are always simple whole number multiples of the fundamental charge!

Coulomb’s Law in an Atom

What is the average electric force between a proton and an electron in a hydrogen atom? (average distance of separation between p+ and e- is 5.3 x 10-11 m)

Answer is 39 orders of magnitude greater than gravitational attraction between the two!

Agenda 1/28/15 DoublesTurn in Coulomb’s Law Lab Final Questions Lab Exit Slip next period

Practice Net Charge and CL Practice Problems for CL Practice Net Charge

Review Everything up to now

HW: Study for Quiz Tomorrow

Agenda 1/29/15Discuss the Review Worksheet Types of Charging Coulomb’s Law

Review Activity for types of charging

Brief Review Quiz

HW: None for tonight

Agenda 1/30/15Review Electrostatics Quiz

Amount of Electrons on a Balloon Lab q = Ne

More Force Practice…maybe

HW: Write up the balloon lab

Agenda 2/4/15Pass Back A LOT!!

Collect Balloon Lab from the rest

Electric Field PhETs Field of Dreams and Field Hockey

Notes of E-Fields and Diagrams Practice Problems

HW: Complete E-Field WS

Electric Fields

Vector quantity

Relates the force exerted on a positive test charge to the size of the test charge

Changes with location

Unit: N/C

E = Coulomb’s force on q’ E = FE

q’ q’

Example ProblemWhat is the strength and direction of the electric field 0.250m to the right of a 1.00C electric charge?

What is the strength of the field .250m to the left of the same charge?

.250m above the same charge?

Electric Field Lines

Arrows show the force direction acting upon a positive test chargeThe more field lines per area, the more intense the electric field is.Notice that arrows flow

out of the positivecharge.

Electric field lines: Multiple Charges

Charges of opposite sign display a watermelon or football-shaped field line structure between them.

Again, arrows flow out of + and into -

Electric field lines: Multiple Charges

Charges of same sign display a diamond- shaped field line structure between them.

Electric field lines: Multiple Charges

Show field lines entering or leaving each charge in the ratio of the relative magnitudes of the charges.

• Above, red charge (+) has 12 lines leaving, blue charge (-) has 6 lines entering, so red charge must have double the magnitude that the blue charge possesses.

Electric field lines: Multiple Charges

More powerful charge tends to dominate the less powerful one and change the basic watermelon/ diamond shape.

Electric Field Lines:Charged Conductors

Two oppositely-charged conducting plates have field lines roughly linear between them and rounded off their edges.

Rules Recap for Drawing E-Field Lines

1. Don’t have field lines cross.

2. Have the same ratio of lines entering/exiting charges as the ratio of the magnitude of the charges

3. Have at least 3 lines entering/exiting all charges

4. Best amount of field lines per charge is from 4-12 lines.

Two

Charge

Examples