PowerPoint Presentation

Its what we seeStatic Electricity

1picture from http://www.boston.com/bigpicture/2008/12/the_year_2008_in_photographs_p.htmlBy Chaiten volcano in Southern ChileChargesRubbing plastic or glass makes them attractive to bits of paper or dust

Benjamin Franklin decided to call the charge on rubbed glass positive

2Top & Bottom

ChargesObjects charged the same way will repel each other

Oppositely charged objects attract each other

4ChargesAll charged objects either attract or repel each other

This implies 2 types of charges

5Check yourself

Two small spheres hung on threads attract one another as shown. It is known that a positively-charged rod will attract ball A.

Ball A has a positive charge.Ball B has a negative charge.III. Balls A & B have opposite charges.

Which of the statements above are correct? Electricity

One of the first objects to hold this charge was amber

The Greek word for amber is elektronElectricityElectron7amber pieceCharge

To understand Charge, lets look at the atomProtons (nucleus) are positively charged(repels charged glass)The electrons are negatively charged(attracts charged glass)8Charge

Even though protons are much bigger (2,000 xs bigger than electron), the and + charges are the same size.If an atom has equal number of electrons and protons the charge is zero.3 electrons (blue) 3 protons (red)Net charge is zero (neutral charge)____?9Charge RulesIn order to be charged, an object must have extra protons or electronsThe following facts help understand charges:In solids, positive charges do not move

protons are fixed in placeBut Negative charges can move10

ConductorsConductors: electrons move throughout the material

Because like charges repel the electrons and protons will be as evenly spaced

Conductors can be charged easily

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Charge RulesInsulators: electrons mostly move around their atom

It is very difficult to charge an insulator because insulators do not allow charges to transfer easily.12Examples of Conductors & InsulatorsConductorsInsulatorsMetals(copper, silver, iron, gold)Human bodiesRubberPlasticGlassCeramics

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Charge RulesIn fluids, both protons and electrons can move all aroundWhat is wrong with this picture?Protons repel protons!

Electrons repel electrons!

Charges need to be distributed evenly throughout the liquid

14water conducts electricityCharge RulesObjects want to be neutral. If given a path to the earth, electrons will flow out until the object is neutral. This is called grounding.

v15Brain Break! Simpsons & ElectrostaticsCharge by RubbingEvery atom attracts electrons (e-) a certain amountWhen you rub two objects together the object that attracts electrons more will steal e-

+17electroscopeCharge by RubbingThis stealer becomes negative (more e-) and the other object becomes positive (lost e-)

What will happen to the charge when the bars separate?18electroscopeTransferring ChargeThis stealer becomes negative (more e-) and the other object becomes positive (lost e-)Only works if there is contact

19use electroscopeConductionA charged conductor touches a neutral conductorTotal Charge = protons - electronsQ1 = -4 Q2 = 0

20use electroscopeConductionA charged conductor touches a neutral conductor

21use electroscopeConductionA charged conductor touches a neutral conductorThe electrons spread out so that the charges on both are equal

Q1 = -2 Q2 = -2 22use electroscopeConductionA charged conductor touches a neutral conductorThe electrons spread out so that the charges on both are equalQ1 = -2 Q2 = -2 23use electroscopeWhat was wrong with this movie?

24use electroscopeInduced PolarityA neutral balloon has no effect on walls e-

How can charged objects attract neutral insulators?

They induce a charge on the neutral object.

25give a balloon a static charge and stick it to the wallinduce => influenceInduced PolarityLets charge the balloon!

Now the e- in the wall are being repelled

This leaves the exposed wall acting positive

Negative and positive charges attract each other

26give a balloon a static charge and stick it to the wallinduce => influence

Induction = Induced Polarity + groundingYou charge an object without touching it with another charged object (conduction)?

Induce polarity with a charged objectGround the objectRemove the ground

Induced polarizationGroundingInduction!27use electroscope

Visualizing Electric Charge pg 183Draw 3 units of charge (protons & electrons)In each barNeutralInduced Polarization pg 183

6 units of charge (protons or electrons)9 protons & 9 electrons totalQ1 = 6Q2 = 0Charge has to equally distribute

Conduction pg 184Q1 = 6What can happen when charged objects touch?

Electrons can transfer!Initially Neutral Q2 = 0Q1 = +3Q2 = +3

Charging by Induction pg 1859 protons & 9 electrons totalProtons attract Electrons

How many electrons should enter from the ground?

The image below is an example of:ConductionInductionInduced Polarization

Charging by rubbingGrounding

The image below is an example of:ConductionInductionInduced Polarization

Charging by rubbingGrounding

The image below is an example of:ConductionInductionInduced Polarization

Charging by rubbingGrounding

The image below is an example of:ConductionInductionInduced Polarization

Charging by rubbingGrounding

Induced polarizationGroundingInduction!The image below is an example of:ConductionInductionInduced Polarization

Charging by rubbingGrounding 36use electroscopeElectrostatic ForceA Force is a push or a pullElectric Force is 1039 times larger than gravityCoulomb studied charge with charged metal balls

Lets look at how the amount of charge on each object and the distance effect the electrostatic force

37use electroscopeCoulombs LawElectrical force is proportional ( ) to both

Particles with more charge (q) experience a greater force.

Charges separated by a smaller distance experience a larger force.38use electroscopeCoulombs LawThese lead to one equation called Coulombs Law:

Electric Force in Newtons (N)charge in Coulombs (C)distance between centers in meters (m)39use electroscopeCoulombs LawA Newton is about equal to poundA Coulomb is the amount of charge in 6.25 x 1018 electrons or protons

40use electroscopeExample 1Two charged spheres, one with 1x1012 extra electrons and one with 2x1012 extra protons are separated by 50 cm. What force do they exert on each other?Given:

Want:

41Example 1 solve for FE

- force is attractive+ force would be repulsive! 42Example 2By what factor does the Electric Force change by if the distance between 2 charged spheres is doubled?Given:

Unknown:

+q+qd+q+q2d

43Time to Check Yourself!pg. 188 #1-6

Skip #9 (unless you want extra credit)44AnswersACACEABADB

5. When two small charged spheres are separated by 2.0 m, the electric force of attraction between them is 6.0 N. If the charge on each sphere is doubled and the separation is reduced to 1.0m, the force of attraction will now be: Given:

Unknown:

46Start Homework!#1-4 pg. 190

Hint: #4)C = 10-6 C

47Discussion Question 1Two identical charges Q, separated by a distance R, feel an electric force F. By what factor does the force change if both charges are doubled (2Q) and the distance is doubled (2d)?(A) 2F(D) F/2(B) 4F(E) F/4(C) FThe Electric FieldAll charged objects produce electric fieldsWe know that a positive charge will repel another positive charge and attract a negative oneIf we draw lines to represent this we would be drawing an electric field

49give a balloon a static charge and stick it to the wallinduce => influenceThe Electric FieldLets look at the rules for drawing field lines:

Field lines always point in the direction that a positive test charge would move+- 50give a balloon a static charge and stick it to the wallinduce => influenceThe Electric FieldField lines always intersect charged objects at right angles+-

51give a balloon a static charge and stick it to the wallinduce => influenceThe Electric FieldField lines always intersect charged objects at right angles+-

52give a balloon a static charge and stick it to the wallinduce => influenceThe Electric FieldField lines never intersect each other+- 53give a balloon a static charge and stick it to the wallinduce => influenceThe Electric FieldThe closer that field lines are to each other, the greater the electric field+54give a balloon a static charge and stick it to the wallinduce => influenceThe Electric FieldExample:Draw the electric Field Lines- +- 55fix animationTime to practiceGo to pg. 25356Electric Field in ConductorsImagine a charged circleWhere can charges move to get farthest away?

57give a balloon a static charge and stick it to the wallinduce => influenceElectric Field in Conductors

Imagine a charged circleWhere can charges move to get farthest away?To the edges!The excess charge on a conductor will always be on the surface58give a balloon a static charge and stick it to the wallinduce => influenceElectric Field in ConductorsHow would the field effect a lone charge in the middle?59give a balloon a static charge and stick it to the wallinduce => influence60

Discussion Question60Why do you think these warnings are on gas pumps? Electric PotentialWhich is worse, 120 volts or 25,000 volts?It depends. Energy causes pain not voltage

Voltage is potential energy per charge

1 volt = 1 Joule of energy per 1 Coulomb of chargeso

61give a balloon a static charge and stick it to the wallinduce => influenceElectric Potential = VoltageBasic outlet is 120 VThe flow of an outlet is about 20 Coulombs/secThe energy released in 1 sec would be:

Amount of energy to lift 75 gal of water 1 m high!

62give a balloon a static charge and stick it to the wallinduce => influenceElectric Potential

Van de Graff generator carries up to 400,000 V!But, it only flows 10 Coulombs/secThe energy released in 1 sec would be:

Amount of energy to lift 2 cups of water 1 m high63give a balloon a static charge and stick it to the wallinduce => influence

Time to practiceGo to pg. 20064