Chapter 11 - Static Electricity

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Chapter 11 - Static Electricity. Day 1. Introduction Sect 11.1 Hw : Questions. Electrostatics The study of electric charge. Charges cannot be created, they can just move; this is how objects become charged . Static Electricity - PowerPoint PPT Presentation

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Chapter 11 - Static Electricity

Chapter 11 - Static Electricity

Day 1Introduction

Sect 11.1

Hw: QuestionsElectrostaticsThe study of electric charge.Charges cannot be created, they can just move; this is how objects become charged.

Static Electricity is electricity that does not move, it stays where the friction happened.Objects can be charged or not charged.POSITIVE ______________NEGATIVE ______________NEUTRAL ______________Draw in neutral, positive, and negative object with 8 total charges in the boxes below.NEUTRALPOSITIVENEGATIVE+-+ -Law of Electric Charges

The Law of Electric Charges states that like charges repel and opposite charges attract.

++/-+++-

Neutral objects have no overall charge. Charged objects attract neutral objects.

Draw a diagram of a negatively charged object brought close to a neutral object. =NEUTRALPOSITIVELY CHARGED +

=NEUTRALInsulators and Conductors

Insulatorsare materials where the charge stays on the spot where you rub the object. They do not let charges move freely (inhibit or prevent the movement of electrons).Ex. Mostly non-metals, rubber (balloon)Used as a safety precaution Ex Protect us from the danger of having large amounts of electric charge move through our bodies if we come in contact with a conductor

Insulators and Conductors

Conductorsare materials that do let charges move freely (allow the movement of electrons).Ex. Most metals, copper, non-pure water (ions)Pure water has NO IONS (ions = charged particles) making them NON-CODUCTIVETap, bottled, and salt water have IONS = CONDUCTIVE

Why is it dangerous to touch an electrical appliance when your near water, wet, or in water (pool, puddle, or bath)?

APPLICATIONS OF CONDUCTOR/INSULATOR COMBINATIONS

Copper wire and plastic for house wiringCar interiors are made or cloth, plastic and leather to insulate passengers from metal body and mechanical parts

Laser Printers contain photoconductors that only allow electrons to flow when laser light shines on it.The laser light quickly draws the image making it negatively chargedThis negatively charged image is then projected onto a selenium drumThe drum then rolls across + charged black plastic powder particles (toner) The toner then becomes attracted to the - charged paper and gets melted onto it.

8Detecting Charge

An electroscope is a device that can detect the presence of charge. Although they can come in many different shapes and sizes, they all achieve the same purpose.

2 Main Types

1.) Pith Ball Electroscope Consists of a ball of pith (plant material) suspended by a thread. Tests for the presence of a charge The ball is neutral, if the object is charged the pith ball will be drawn towards it.

2.) Metal Leaf Electroscope

There are two lightweight strips of metal that bend easily.These leaves are attached to a central metal rod with a metal sphere at the top. Since the sphere, rod, and leaves are all metal (conductors) electrons can move freely within them.When the metal leaves become charged (positively or negatively) they become charged the same and therefore repel each other. The metal leaves moving away from each other is proof they are both chargedPg. 471 Q: 3-9

Day 2Sect 11.2 - Pg. 482PPT: Charging by CONDUCTIONBell Work (have HW questions out) How might technology be enhanced with the use of electricity? How might technology be improved with our new knowledge of the law of electric charge?How might yesterdays lesson prove helpful in the future? Improve efficiency, duration, renewable* cant be created or destroyed just transferred

Opposite charges attract improve efficiency of some processes by giving things a charge (ie. Paint) Same charges repel could be used to increase resistance btw objects, prevent sticking (paint example extended)

Safety insulators vs. conductors (ie electricity in your house, fuse box), telephone wire on car example, 12ReviewStatic electricityStationary (no free flow of electrons) Law of electric chargeOpposites attract, same charge repel Insulators vs. conductorsOne allows movement one preventsElectroscopeTwo typesPith ball & metal leaf HWPg. 471 Q: 3-9

3. a) Which particles are difficult to add or remove from an atom? Protons and neutronsb) Which are easier to add or removeElectronsc) How does a/b explain the formation of + and charged objects?Illustrates that electrons can move (leave their atom) and move into another, creating a imbalance of charges (- if added, + if removed)

HW4. Describe the total charge on each of the following objects as either neutral, positive, and negatively charged13- the object is neutral balance of charges14 Negative because more than + 5. What would you do to the object in fig 15 to make it neutral? Add 2 negative charges to balance it 6. What would you do to make it + charged? charged?Remove electrons = +, add electrons = - HW7.Would the following repel or attract? + beside a Opposites attract - beside a Like charges repel 8. a) how does a electrostatic pain sprayer work? Paint = +, surface = - attraction ensures coverageb) Are they beneficial? Yes. Reduce amount of misses spots/paint usedCharging by Conduction

Neutral objects can become charged through conduction in two different ways charging by friction (1) and charging by contact (2).

1. Charging by FrictionWhen you rub two different neutral objects together, they become charged.One material is more likely to gain electrons becoming negatively charged.The other material is likely to give up electrons becoming positively charged.

How does the air effect an objects charge? Humid air has more water, collisions btw water and nearby charged objects cause a transferring of electrons and a reduction of charge. How would one determine which of the neutral objects will become positively charged and which one will become negatively charged?Use the Electrostatic Series which is a list of materials in order from those with a weak attraction for electrons to those with a strong attraction for electrons.Pg. 473 Electrostatic SeriesAirHuman hands/skinRabbit fur Nylon / WoolHuman Hair / Cats Furcalcium, magnesium, leadsilkaluminum, zincCottonAmberAcetate / RayonPolyesterCellophane tape SaranVinyl / TeflonSilicon Rubber

Weak hold on electrons-Tendency to lose electronsStrong hold on electrons-Tendency to gain electronsHow to Use the Electrostatic Series

You can use the list to determine the charges that will appear when two objects are rubbed together. Remember these rules!Objects high on the list LOSE ELECTRONS easily, therefore, they develop POSITIVE charge after being rubbed.Objects low on the list GAIN ELECTRONS easily, therefore, they develop a NEGATIVE charge after being rubbed.When determining charges of rubbed objects, locate them on the list. The one higher on the list will be POSITIVE and the one lower on the list will be NEGATIVE.

Charging by Conduction (Friction)

As we have learned, objects can be charged by friction. (REVIEW)When two neutral objects are rubbed together, one becomes positively charged and the other becomes negatively charged. The electrostatic series allows you to predict the charge of each object.

Charging by Conduction (2. Contact)

Objects can also be charged by contact. When a charged object touches a neutral object the neutral object gets the same charge. This occurs because the electrons move from one object to the other

+++++++++++++-----------------electronsnegatively charged-Draw a picture of a neutral pith ball being charged by contact by a positively charged object.

If two charged objects come in contact, the electrons will move along a CONCENTRATION GRADIENT from an area of high concentration (Neg.) to an area of lower concentration (Pos.)Produces a more EVEN distribution of electric charge btw the two objects.

Grounding

removing excess charge (either positive or negative) involves transferring electrons between the object and a large neutral object such as Earth (the ground)infinite reservoir of electrons = charge is spread out and neutralized

The Symbol for Grounding =

HW: Pg. 477 #1,2,5,6

24Day 3: LabReview Yesterday & Take up HW HANDOUT: Lab Charging by ConductionKey TermsGroundingRemoving excess charges via the groundElectrostatic SeriesList of materials based on likeliness of giving/taking electronsConduction Charging something involving touch - 2 types Friction rubbing two different materialscontact a charged object touching another objectHW: Pg. 477 #1,2,5,6 predict the following pairs = PositiveGlass and silkEbonite and furHuman hair and rubber balloonAmber and cotton Why do objects made from different materials develop an electric charge when rubbed? What is this method called?Friction one gives up ELECTRONS, the other takes them (based on electrostatic series) HW: Pg. 477 #1,2,5,6 5. Two rods, X (+8) and Y (-4) touchWhat particles moved?electronsWhat rod did the particles move from? Y only electrons move. Concentration gradient area of high concentration to an area of low, with respect to the excess of ELECTRONS6. Describe how electrons travel when a positively charged object is grounded. Electrons would be PROVIDED by the earth (infinite reservoir), and supplied to the charged object until it became neutral Day 4 : Review

PPT Note: Charging by INDUCTIONREVIEW: Charging by CONDUCTION1: Friction - Rubtwo different neutral objects rub together to create frictionone material readily gives up electrons to become positively charged while the other takes electrons to become negatively charged *(refer to electrostatic series)materials oppositely charged will attract according to the Law of Electric Charge

2: Contact - Touchan already charged material contacts a neutral oneelectrons flow into or out of the neutral material depending on the type of charge present in the charged material the neutral object will become charged identically to the charged object and they will immediately repel each other

29Charging by inductionSect. 11.6

Since we now know what charging by CONDUCTION means what do you think INDUCTION refers to?

What are some applications of this technology? Charge cell phones without cords. Charge electric cars while driving!30Charging by Induction 11.6

Charging by induction indicates that there is an approach of an object but no contact.

There are two forms of Charging by Induction TemporaryPermanent

Footprints at a Crime Scene (Electrostatic Lifting Apparatus ESLA)A film paper is charged and placed over the footprintDirt particles from the footprint jump up and attract to the paper leaving the footprint outlineElectrostatic Sound SpeakersThe rapid vibration (back and forth motion) of a charged paper or plastic cone (called a diaphragm) produces sound waves in the air that we hear. The back and forth movement is the result of the diaphragm attracting and repelling two charged plates that are always having their charges reversed by a transformer that is connected to the plates.These speakers are thin and light. Good for treble, not so good for bass.HW p. 489 #1-6

31A) Temporary charge by induction

occurs when a charged object approaches a neutral one. When they are very close, electrons of the neutral material move within the object which sets up a polarity. Also called induced charge separation or ICSInduced Charge Separation (ICS)

The electrons in the neutral object move to one end or the other (depending on whether the charged object is + or -) in order to create attraction.Once the charged object is removed, the electrons in the neutral object return to their original state.

Neutral Pith Ball & Neg. Rod

Neutral Pith Ball & Pos. Rod

------------++++++++++++Electrons in electroscope move downleaves become ve and repelleaves become +ve and repelElectrons in electroscope move upCharging by Induction

34A) Temporary charge by induction

The neutral object becomes temporarily charged positive at one end and negative at the other (ICS). Since the induced charge is opposite the charge of the charged object, the two objects will attract.

*Once the original charged object is taken away, the electrons in the neutral object return to their normal arrangement.

B) Permanent charge by induction

Can happen via a ground wire. During the approach of the charged object, a ground wire is touched to the neutral material (to whatever side the electrons will shift to). The wire allows excess electrons to escape or supply additional electrons according to the type of charge on the charged object.

+++++++++--------+++++++++----------------

Induced Charge Separation

4 Stages

This sets up 2 attractions: 1 - btw the pith ball and the negative rod2 btw the ground and the and pith ball via the grounding wire

The electrons from the rod cant jump (not strong enough) but what about the pith balls electrons?37

Induced Charge Separation

4 Stages

This sets up 2 attractions: 1 - btw the pith ball and the negative rod2 btw the ground and the and pith ball via the grounding wire

The electrons from the rod cant jump (not strong enough) but what about the pith balls electrons?38

B) Permanent charge by induction

After the ground wire is used, the charged material is removed. In this method of charging, the induced charge will always be the opposite of the original charged material. In order for the charge to be permanent, the ground wire must be disconnected or removed before the charged object is removed.

HW477 #1-3, 5, 6

489 #2, 5ReviewOn a blank page Compare and Contrast charging by INDUCTION vs. CONDUCTIONTreat this as a test scenario Write down what you know without your notesUse your notes afterwards to fill in any missing important infoExchange with a peerCorrect spelling, grammar, and any missing infoCHARGING REVIEWConduction VS.Via contactFRICTIONRubbing two diff. neutral objectsRelies on electrostatic seriesCONTACTOne charged one neutralNeutral object will obtain the same charge (electrons move down concentration gradient)

InductionWithout contactTEMPORARYInduced charge separationCharged object approaches neutral object, a temporary polarity (north vs. south pole) sets upPERMANENT Induced charge separation with a grounding wireGrounding wire provides electrons (if charged object is positive) or removes them (if charged object is negative)Cutting the grounding wire maintains the temporary charge created43HWTake up any questions/concerns with HW from any student that completed the assigned HW11.8 - Electric Discharge(pg. 492)

11.8 - Electric Discharge (pg. 492)

Def. Electric Discharge Rapid transfer of excess charge btw two objects

When two objects that have a charge imbalance (concentration gradient) are near each other or come in contact, electrons travel down the concentration gradient (from an area of high electron conc. to an area of low electron conc.)

Can be visible as sparksGreater the imbalance, greater/more noticeable the discharge Discharges superheat the air around them, potentially causing burns or damaging electronic equipment

Think/Pair/Share 3 minLightning How is lighting created or how does it work?

Lightning Rods How do they work? Why do we need them?

Lightning

As water molecules move past each other they become chargedFalling drops pick up electrons lower half the cloud negative, upper positiveExcess negative charge in the lower cloud repels the electrons in the earths surface creating a?

Induced Charge Separation (ICS)

hint: low to high pressure49++++++++++++++5. electrons collide with air creating heat & light3. negative charges in clouds repel negative charges on the earthearth surface (induction) = positively chargedLightning 4. negative charges jump from the cloud to the earth 1. particles in clouds rub together causing charged particles 2. negative charges collect at the bottom of the cloud+++++++++++++++5050Lightning

This creates a charge imbalance or a?

Once the imbalance is great enough, a discharge btw the cloud and the ground occurs Or btw clouds, or from earth to cloud

hint: low to high pressure

Lightning travels at 300,000 kilometers/sec. Thunder travels 330 meters/sec. You can count the time from seeing the lightning to hearing the thunder. Lightning travels so fast you can ignore its speed. Just use the spped of sound. Count the seconds between seeing the lightning and hearing the thunder, and multiply by 330 to get how many meters away it was (or divide this by 1000 to get kilometers). 51What is happening here?

Lightning in Space?

Lightning is caused by a current of electricity through a dense gas such as air. The current excites the atoms of the air to emit a brilliant light that we see as lightning. Very large electric currents also flow through space. For example the solar wind is a current of charged particles. However there is not enough gas in space to cause the flash that we recognize as lightning. When this current strikes the rarefied outer parts of the earth's atmosphere, it causes a soft glow known as the aurora. Similar currents may emerge from other phenomena in space. When they strike a nebula they cause the beautiful coloured glows that we are familiar with from hubble pictures.

52Lightning Rods

Lightning travels along the path of least resistance (easiest path electrons can find) Lightning rods are composed of highly conductive metals (iron or copper) that goes from a high object (top of house or barn) and reroutes it to the earth (grounding)

ICS+++lightning bolt strikes rodcharges travel from the rod, through the wire and into the ground

Lightning Rods++++++++++Chapter ReviewChapter 11 ReviewPg. 498 - Q 1, 2, 3, 6, 7, 10, 11, 15, 16, 18, 22, 23, 28, 29, 31

Self quizPg. 500 Q 1-23