It’s what we see… Static Electricity

Charges Rubbing plastic or glass makes them attractive to bits of paper or dust Benjamin Franklin decided to call the charge on rubbed glass positive

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Charges Objects charged the same way will repel each other Oppositely charged objects attract each other

Charges All charged objects either attract or repel each other This implies 2 types of charges

Check yourself Two small spheres hung on threads attract one another as shown. It is known that a positively-charged rod will attract ball A. I.Ball A has a positive charge. II.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 elektron o Electricity o Electron

Charge To understand Charge, let’s look at the atom Protons (nucleus) are positively charged (repels charged glass) The electrons are negatively charged (attracts charged glass)

Charge Even though protons are much bigger (2,000 x’s 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) ____?

Charge Rules In order to be charged, an object must have extra protons or electrons The following facts help understand charges: 1.In solids, positive charges do not move protons are fixed in place But… Negative charges can move

Conductors Conductors: electrons move throughout the material Because like charges repel the electrons and protons will be as evenly spaced Conductors can be charged easily

Charge Rules Insulators: electrons mostly move around their atom It is very difficult to charge an insulator because insulators do not allow charges to transfer easily.

Examples of Conductors & Insulators ConductorsInsulators Metals (copper, silver, iron, gold) Human bodies Rubber Plastic Glass Ceramics

Charge Rules 2.In fluids, both protons and electrons can move all around What is wrong with this picture? Protons repel protons! Electrons repel electrons! Charges need to be distributed evenly throughout the liquid

Charge Rules 3.Objects want to be neutral. If given a path to the earth, electrons will flow out until the object is neutral. This is called grounding. v

Brain Break! FSimpsons & Electrostatics

Charge by Rubbing Every atom attracts electrons (e - ) a certain amount When you rub two objects together the object that attracts electrons more will steal e − −

Charge by Rubbing This stealer becomes negative (more e - ) and the other object becomes positive (lost e - ) What will happen to the charge when the bars separate?

Transferring Charge This stealer becomes negative (more e - ) and the other object becomes positive (lost e - ) Only works if there is contact

Conduction ① A charged conductor touches a neutral conductor Total Charge = protons - electrons Q 1 = -4 Q 2 = 0

Conduction ① A charged conductor touches a neutral conductor

Conduction ① A charged conductor touches a neutral conductor ② The electrons spread out so that the charges on both are equal Q 1 = -2 Q 2 = -2

Conduction ① A charged conductor touches a neutral conductor ② The electrons spread out so that the charges on both are equal Q 1 = -2 Q 2 = -2

What was wrong with this movie?

Induced Polarity A neutral balloon has no effect on wall’s e - How can charged objects attract neutral insulators? They induce a charge on the neutral object.

Induced Polarity Let’s 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

Induction = Induced Polarity + grounding You charge an object without touching it with another charged object (conduction)? 1.Induce polarity with a charged object 2.Ground the object 3.Remove the ground Induced polarization Grounding Induction!

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

Induced Polarization pg units of charge (protons or electrons) 9 protons & 9 electrons total Q 1 = 6 Q 2 = 0

Charge has to equally distribute Conduction pg 184 Q 1 = 6 What can happen when charged objects touch? Electrons can transfer! Initially Neutral Q 2 = 0 Q 1 = +3 Q 2 = +3

Charging by Induction pg protons & 9 electrons total Protons attract Electrons How many electrons should enter from the ground?

The image below is an example of: A.Conduction B.Induction C.Induced Polarization A.Charging by rubbing B.Grounding A.Conduction B.Induction C.Induced Polarization A.Charging by rubbing B.Grounding

The image below is an example of: A.Conduction B.Induction C.Induced Polarization A.Charging by rubbing B.Grounding A.Conduction B.Induction C.Induced Polarization A.Charging by rubbing B.Grounding

The image below is an example of: A.Conduction B.Induction C.Induced Polarization A.Charging by rubbing B.Grounding A.Conduction B.Induction C.Induced Polarization A.Charging by rubbing B.Grounding

The image below is an example of: A.Conduction B.Induction C.Induced Polarization A.Charging by rubbing B.Grounding A.Conduction B.Induction C.Induced Polarization A.Charging by rubbing B.Grounding

Induced polarization Grounding Induction! The image below is an example of: A.Conduction B.Induction C.Induced Polarization A.Charging by rubbing B.Grounding A.Conduction B.Induction C.Induced Polarization A.Charging by rubbing B.Grounding

Electrostatic Force A Force is a push or a pull Electric Force is times larger than gravity Coulomb studied charge with charged metal balls Let’s look at how the amount of charge on each object and the distance effect the electrostatic force

Coulomb’s Law Electrical force is proportional ( ) to both Particles with more charge (±q) experience a greater force. Charges separated by a smaller distance experience a larger force.

Coulomb’s Law These lead to one equation called Coulomb’s Law: Electric Force in Newtons (N) charge in Coulombs (C) distance between centers in meters (m)

Coulomb’s Law A Newton is about equal to ¼ pound A Coulomb is the amount of charge in 6.25 x electrons or protons

Example 1 Two charged spheres, one with 1x10 12 extra electrons and one with 2x10 12 extra protons are separated by 50 cm. What force do they exert on each other? Given: Want:

Example 1 solve for F E - force is attractive + force would be repulsive!

Example 2 By what factor does the Electric Force change by if the distance between 2 charged spheres is doubled? Given: Unknown: +q d 2d

Time to Check Yourself! pg. 188 #1-6 Skip #9 (unless you want extra credit) pg. 188 #1-6 Skip #9 (unless you want extra credit)

Answers 1.A 2.C 3.A 4.C 5.E 6.A 7.B 8.A 9.D 10.B 1.A 2.C 3.A 4.C 5.E 6.A 7.B 8.A 9.D 10.B

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:

Start Homework! #1-4 pg. 190 Hint: #4)μC = C #1-4 pg. 190 Hint: #4)μC = C

Discussion Question 1 Two 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) F Two 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) F

The Electric Field All charged objects produce electric fields We know that a positive charge will repel another positive charge and attract a negative one If we draw lines to represent this we would be drawing an electric field

The Electric Field Let’s look at the rules for drawing field lines: ① Field lines always point in the direction that a positive test charge would move

The Electric Field ② Field lines always intersect charged objects at right angles

The Electric Field ② Field lines always intersect charged objects at right angles

The Electric Field ③ Field lines never intersect each other

The Electric Field ④ The closer that field lines are to each other, the greater the electric field

The Electric Field Example: Draw the electric Field Lines

Time to practice Go to pg. 253

Electric Field in Conductors Imagine a charged circle Where can charges move to get farthest away?

Electric Field in Conductors Imagine a charged circle Where can charges move to get farthest away? To the edges! The excess charge on a conductor will always be on the surface

Electric Field in Conductors How would the field effect a lone charge in the middle?

60 Discussion Question 60 Why do you think these warnings are on gas pumps?

Electric Potential Which 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 charge so

Electric Potential = Voltage Basic outlet is 120 V The flow of an outlet is about 20 Coulombs/sec The energy released in 1 sec would be: Amount of energy to lift 75 gal of water 1 m high!

Electric Potential Van de Graff generator carries up to 400,000 V! But, it only flows 10 μCoulombs/sec The energy released in 1 sec would be: Amount of energy to lift 2 cups of water 1 m high

Time to practice Go to pg. 200