Is For Electricity. fundamentals that drive our world.

Is For Electricity

fundamentals that drive our world

Charge It!!!What is evidence of charge?What are the two kinds of charge?What are the three ways for and object or

material to become charged?

HW: Learn 194-201 At least 6 talking to the text points.

The Mighty AtomSince there arean equal

numberof electrons

andprotons, the net charge onthis atom is 0.

The Mighty AtomThe only way for it

to become charged is to gain or lose electrons.

Two Types of ChargeNEGATIVE (-) : More electrons than protons or

an excess of electrons.POSITIVE (+): Fewer electrons than protons or

a deficit of electrons.NEUTRAL – Is a state of charge, NOT A TYPE

OF CHARGE!Neutral is equal amounts + and -.

Quick CheckWhat is the charge on each atom?

Charging Can Be Done By..FRICTION:Rubbing two objects together to remove or

deposit electrons.CONTACT:Touching one charged object to a neutral to

remove or deposit charge.INDUCTION:Bringing one charged object near a neutral so

charges polarize or separate.

The Fundamental ConceptNo matter what – the net charge in any process

is always zero.Charge is always conserved.One object might lose charge to another, but

the pair of objects still has a net charge of zero.

Sign Convention

How Charges Interact

How Objects Interact

Proof Is In The Pudding

Proof Is In The Pudding

Quick Check

InsulatorsRubbing wool over

the R, tape reacted near the R but not near the N.

Charge was localized (stuck) near the R and couldn’t move over to the N.

NR

Conductors

The Pie PlatesThe key to getting a

net charge on the pie plate is to touch it so electrons rush from the plate leaving it with a net + charge.

Conductors & InsulatorsCONDUCTORS:Allow charges to pass through them.Induction causes charges to separate.Charges will become evenly distributed on the

surface of a conductor.

Conductors & InsulatorsINSULATORS:Do not allow charges to pass through them.Induction causes atoms/molecules to polarize.Charges will become stuck in certain regions of

the material.

Quick Check

Polarization of Insulators

Polarization of Conductors

Neutrals Will Be Attracted!

Quick CheckCharged rubber rods are placed near a

neutral conducting sphere, causing a redistribution of charge on the spheres. Which of the diagrams below show the proper distribution of charge on the spheres? List all that apply.

Charge It!As we have seen that charges behave

differently in different materials due to the nature of the bonds involved.

Metallic bonds allow electrons to flow freely whereas covalent bonds do not.

The dividing line is the metalloids on the Periodic Table.

(Thought you were done with chem, eh?!?!)

Excuse Me Mr. Coulomb, But Would You Like To Charge That?Like gravity, charges exert forces over a

distance. So perhaps we can use gravity as an analog to forces created by charges.

Coulomb’s Force PendulumA positively charged metallic

sphere is hung from a non conducting thread.

An equally charged negative sphere is brought near by.

Coulomb’s Force PendulumA positively charged metallic

sphere is hung from a non conducting thread.

An equally charged negative sphere is brought near by.

The other sphere shifts towards it.The angle is proportional to the

relationship of Fe , mg and separation distance r.

+

mg

Fe

θ

d

Coulomb’s Force PendulumWe know the equation of

gravity

F = G

r

mg

Fe

θ

m1m2

d2

L

d

Coulomb’s Force PendulumWhich brings us to this for

small angles:We can use similar triangles to

relate the two kinds of forces.Fe/d =mg/LFe/mg = d/LWhich says that gravity and the

electric force are directly related.

r

But what about r? mg

Fe

θL

d

Coulomb’s Force Pendulum

Some Simulationshttp://webphysics.davidson.edu/physlet_resources/bu_semester2/index.html

Coulomb’s Force PendulumSince they are directly related

we conclude both follow the inverse square law.

Fe = k r

mg

Fe

θ

Lq1 q2

r2

Coulomb’s Law

Where q is charge measured in coulombs which must be noted as + or - charges

r is separation distance in metersk is a constant 9 x 109 N·m2/C2

Fe = kq1 q2

r2

How Big Is A Coulomb?The charge on an electron (e-)−1.602176487×10−19 CAnd a proton (p+)+1.602176487×10−19 CIt takes 6.2414 ×1018 electrons to = 1CFor singly ionized water that’s .000187 gramsImagine the amount of charge a few grams

would hold and you understand a lightning bolt!

A mole of e- = 96,484 C. Holy @#&*$!

Field of Dreams, Part ICharges and charged objects generate electric

fields.These fields can be thought of as vectors

passing through empty space.How the field vectors interact is how forces of

attraction and repulsion are transferred.We can’t see these fields, only observe their

interaction with other objects.Perhaps a look at gravity would help.

Electric Field Strength

Coulombs Law

Fg

= G

Gravity

Fe = kq1 q2

d2

m1 m2

d2

Electric Field Strength

Coulombs Law

Fg

= G

When these terms are collected we get g the acceleration due to gravity, 9.81 m/s2 leaving us with the familiar F = mg.

Fe = kq1 q2

d2

m1 m2

d2

Electric Field Strength

These terms collect to form a notation of field strength called the Electric Field Intensity, E, which is a vector field, + or -.

F = EqWhere E is measured in N/C.

Fe = kq1 q2

d2

Electric Field NotationTo note a field we typically show a line (or

plate) with a vectors as field lines.

+

Projectile Motion LinkShoot a charge through the field and it will

curve.

+ -

Fields Created By Chargeshttp://www.falstad.com/emstatic/

http://www.falstad.com/vector2de/

http://www.falstad.com/vector3de/

Force Related to DistanceLift an object and do work against gravity…..Hey that sounds familiar!!!!!!!!!!!It’s work against gravity, or PE.Wonder if it works for moving a charge in an

Electric field?

Work Done On ChargesPE = mgh

E is similar to gh is similar to r or dm is similar to q

Bowling Ball

Work Done On ChargesI can say that I did so

many joules of work, total.

PE =mgh W = FdOr I could say I did so

many joules of work on the ball.

PE = Joules/ BB

Bowling Ball

Work Done On ChargesEach ball has the same PE.The more balls the greater

the potential to wreak havoc on the floor.

Total PE = 3 x (J/BB) Or 3 J/BB

Bowling Ball

Work Done On ChargesIf I imagine that each BB is

equal to one coulomb of charge we can write this:

PE = J/C

Volt = J/C

Bowling Ball

Work Done On ChargesVolt = J/CWhich is called POTENTIAL.

Bowling Ball

A Return to Gravity

Coulombs Law

F = G F = mg

Fe = k F = Eqq1 q2

d2

m1 m2

d2

Coulombs Law In New WayFe = k (I)

F = Eq E = F/q (II) subbing II into I

E = kq/r2 (III)

q1 q2

d2

Work Done To Move A Chargehttp://webphysics.davidson.edu/physlet_resources/bu_semester2/index.html

Work On A ChargeW = Fd …………. W = Fed (I)

Fe = Ed E = Fe/q E = k q/r2 (II)

Working a number of substitutions of the these 5 expressions brings some more

W = qV V = k q/r