The Characteristics D - WordPress.com › 2019 › 03 › unit... · 2019-03-25 · 2. Add categories, terms, concepts, and sketches to the map, making links between the parts that

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The Characteristicsof ElectricityThe Characteristicsof Electricity

Lightning flashes aroundtransmission linescarrying electricity tocommunities.

U N I T

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Unit Task

In your Unit Task, you will evaluate methods of localelectricity generation that could be used as backupsources for the regional power grid. Your investigationsinto the characteristics of electricity, methods ofconserving electrical energy, and methods of providingelectrical energy will help prepare you for your task.

Essential QuestionHow can we use local resources to generate electricityin a dependable, environmentally friendly way?

Static charges collect on surfaces andremain there until given a path to escape.

10.1 Exploring the Nature of Static Electricity

10.2 The Transfer of Static Electric Charges

10.3 Electrostatics in Our Lives

Current electricity is the continuous flow ofelectrons in a closed circuit.

11.1 Current, Potential Difference, and Resistance

11.2 Series Circuits and Parallel Circuits

11.3 Ohm’s Law

We can reduce our electrical energyconsumption and use renewable energyresources to produce electrical energy.

12.1 Renewable and Non-Renewable EnergyResources for Generating Electricity

12.2 Reducing Our Electrical Energy Consumption DI

DI

DI

Contents

10

11

12

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Toronto was one of many cities that were without electricity during the 2003 blackout.Some places in Ontario now celebrate Blackout Day on August 14 to remind people ofhow important it is to conserve energy.

Blackout!Imagine what it would be like to live in a world withoutelectricity. Now, count to nine. In a mere nine seconds, thatscenario came true. On August 14, 2003, at 4:11 in the afternoon,50 million people in Ontario and the northeastern United Stateswere plunged into the largest electrical blackout in NorthAmerican history. Elevators stuck between floors, subways werein blackness, traffic lights stopped working, and television screensand computer monitors went dark.

Electricity is often generated far from cities and is distributedalong a network that includes electrical generating stations,transmission lines, and distribution stations. This huge,interconnected system of electricity networks is called the“energy grid.” Ontario, New York, Michigan, and othernortheastern provinces and states are part of the easterninterconnection grid.

Electricity cannot be stored for long after it is generated, so allparts of the grid must maintain a balance of supply and demand.If a transmission line or generator is overloaded, that part of the

390 UNIT D The Characteristics of Electricity

Exploring

Electrical generatingstations from Ohioto Ontario shutdown, leaving50 million people in the dark. Why?

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391Exploring

energy grid is disconnected automatically and the electricity issent along alternative paths. One cause of problems in an energygrid is transmission lines that touch trees so that the electricitymoves through the trees into the ground instead of along the wire.

Preventing Future BlackoutsOn August 14, a series of events, including human error, highdemand, lines touching trees, automatic shutdowns, and failuresof alarm systems, resulted in a huge surge of electricity in thegrid. Within seconds, 256 electrical generating stations from Ohioto New York to Ontario shut down as a protective control. It tookalmost two full days to get all the generating stations back inoperation and electricity restored to all the affected areas.

This blackout raised difficult questions that could only besolved by government and electrical industry experts from bothCanada and the United States working together. How did theblackout happen? What can be done to prevent such a blackoutfrom occurring again? These are very complex questions toinvestigate.

By working cooperatively, groups from the two countriessuccessfully figured out the answers to these questions. Now,because of their hard work, the electrical grid is safer and betterable to deal with a similar situation. Smaller, local blackouts dooccur from time to time. But the knowledge learned from themistakes of previous large blackouts helps reduce the chances ofsuch a large-scale blackout happening again.

D1

Electricity Concept Map

Electrical energy is often in the news. You haveprobably read or viewed reports about the costsand benefits of producing energy from renewableand non-renewable sources. You might bepractising some ways to reduce electrical energyconsumption and achieve electrical savings inyour home. And you can probably describe theimportance of electricity to your daily life.

Now is your opportunity to get a sense of howyour pieces of knowledge about electricity fittogether.

1. As a class, create a concept map aboutelectricity. Start with the word “electricity” inthe centre of a large piece of chart paper.

2. Add categories, terms, concepts, andsketches to the map, making links betweenthe parts that are connected.

Science, Technology, Society, and the EnvironmentSTSE

A transmission line is automaticallydisconnected from the grid when ittouches treetops or other objects.

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10 Static charges collect on surfaces and remain there until given a path to escape.

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Static charges collect on surfaces and remain there until given a path to escape. 393

Sparks flash from the centre of a plasma ball to thepoint of contact where a hand touches the ball.

Skills You Will UseIn this chapter, you will:

• investigate the transfer of static electric charges by friction,contact, and induction

• predict the ability of different materials to hold or transferelectric charges

• plan and carry out inquiries to determine and compare theconductivity of various materials

• apply knowledge and understanding of the safe operationof electrical equipment

Concepts You Will LearnIn this chapter, you will:

• learn about the differences between electrical insulatorsand conductors

• explain how materials allow static charges to build up or todischarge

• analyze the design of technological devices that improveelectrical efficiency or protect other devices by using orcontrolling static electricity

Why It Is ImportantStatic electricity is part of our daily lives. By understandinghow charges build up and discharge, we can avoid problemscaused by sparks and make use of static electricity toimprove our lives.

Determining Importance

Preview the subheadings and illustrations in Chapter 10.Which topics and illustrations are familiar? Which topicsand illustrations are unfamiliar based on yourbackground knowledge and experience? The unfamiliartopics and illustrations represent the information that ismost important for you to learn. Create a list of learninggoals for this chapter based on the information thatrepresents new learning for you.

Key Terms

• conduction • conductor • electrical discharge• electron • electron affinity • friction • induction • insulator • static electricity

Before Reading

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A Shocking ExperienceOn a cold winter day, you have probably pulled a sweater off overyour head or removed your hat and felt your hair flying up. Ormaybe you have reached to touch a doorknob or the door handleof a car and received an electric shock. These examples and hair-raising experiences like the one in Figure 10.1 are caused byelectric charges. Electric charges are charged particles that exertan electric force on each other. These charged particles are verysmall. In fact, there are millions of them on each standing hair inthe picture above.

The accumulation or gathering of even larger numbers ofelectric charges can lead to some impressive electrical displays.Think back to the last time you observed a lightning storm. Thelarge, bright flashes of lightning look like the small electric sparksyou may have seen when touching the doorknob or taking offyour sweater. In fact, they are the same thing, just different insize. These are all examples of static electricity.


Here is a summary of what youwill learn in this section:

• Solid materials are charged bythe transfer of electrons.

• When an atom gains electrons,it becomes negatively charged.

• When an atom loses electrons,it becomes positively charged.

• Electrons can be removed fromobjects through friction.

• Particles with unlike chargesattract each other, andparticles with like charges repeleach other.

• Electrical insulators andconductors are materialscategorized by how freely theyallow electrons to move.

Exploring the Nature of Static Electricity

Figure 10.1 Electric charges cause strands of hair to repel each other and be attracted to theballoon.

10.1

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395Static charges collect on surfaces and remain there until given a path to escape.

D2 Quick Lab

Characteristics of Electric Charge

A characteristic is a distinguishing trait or quality of asubstance or object.

PurposeTo observe the characteristics of electric charge

Procedure

1. Read through the procedure steps, and makepredictions about what you think will happen ineach step. Record your predictions.

2. Sprinkle some confetti or gelatin powder in asmall area on your desk. Push a plastic drinkingstraw through your hair several times, and bring itclose to the confetti or gelatin powder. Recordyour observations.

3. Inflate two balloons, and knot the ends. Rub oneside of each balloon on your hair or clothing.Hold the balloons by the knots, and bring therubbed surfaces slowly together. Observe theresults.

4. Turn one balloon so that its rubbed surface facesaway from the other balloon. Again bring theballoons together. Record your observations forsteps 3 and 4.

5. If your classroom has a Van de Graaff generator,your teacher will demonstrate the followingexperiments by putting the materials for eachexperiment in place and then turning on thegenerator. Record your observations for eachexperiment.

(a) Tape one end of the thin paper strips to theVan de Graaff generator.

(b) Place a stack of three aluminum pie plates onthe Van de Graaff generator.

(c) Place a clear plastic cup full of polystyrene“popcorn” on the Van de Graaff generator.Put a loose-fitting lid on top of the cup.

(d) Attach a metal rod to a lab stand, and place itclose to the Van de Graaff generator.

6. Return everything you used to the areasdesignated by your teacher.

Questions

7. (a) Which objects were attracted to each other?

(b) Which objects were repelled or pushed awayfrom each other?

8. How did your observations compare with yourpredictions for each step?

9. What do you think caused the movements thatyou observed?

Materials & Equipment• confetti or gelatin powder

• plastic drinking straw

• 2 balloons

• Van de Graaff generator

• thin paper strips

• clear adhesive tape

• 3 aluminum pie plates

• clear plastic cup with lid

• polystyrene “popcorn”

• metal rod and lab stand

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Electrically Charged ParticlesYou may recall from earlier studies that an element is a puresubstance that cannot be broken down into simpler substances. Anelement is made up of tiny particles called atoms. An atom is thesmallest part of an element with the element’s properties. Withinan atom, there are three types of smaller particles: protons,neutrons, and electrons. Protons and electrons are electricallycharged particles. Protons have a positive electric charge (+), andelectrons have a negative electric charge (–). Neutrons have noelectric charge, so they are neutral. The protons and neutrons are inthe nucleus at the centre of the atom. The electrons are outside thenucleus (Figure 10.2).

Although they contain electrically charged particles, atoms areneutral. The number of protons in the nucleus equals the numberof electrons around the nucleus, so the number of positive andnegative charges is equal. This makes an atom neutral.

Static ChargesObjects can become charged when electrons move from one objectto another. The electric charge that builds up on the surface of theobject is called a static charge or static electricity. The chargesare “static” because they remain very nearly fixed in one locationon the surface of the object until they are given a path to escape.

An object that has more electrons than protons is negativelycharged. An object that has more protons than electrons ispositively charged. You can group objects according to three kindsof charge: positive, negative, and neutral. If a neutral object obtainsextra electrons, the object becomes negatively charged. If a neutralobject loses electrons, the object becomes positively charged.


neutron proton

nucleus

electron

Figure 10.2 Each atom is made up of protons and neutrons inside the nucleus and electronsin the area around the nucleus.

WORDS MATTER

“Static” is from the Greek wordstatikos, meaning causing to stand.The word “stationary,” which meansnot moving, is based on the sameGreek word.

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Friction and the Movement of ElectronsAll solid materials are charged by the transfer of electrons. Howdo atoms lose or gain electrons to become electrically charged?One common cause of electron transfer is friction, which occurswhen objects rub against each other.

Friction is the force resisting the relative motion of twosurfaces in contact. When two objects rub together, the force offriction can remove electrons from one object and cause them totransfer to the other object. As one object loses electrons, theother object gains them, as shown by the amber and fur in Figure 10.4.

If you count the electrons in Figure 10.4, you will notice thatno electrons are lost during the process of charging. They aresimply transferred. The position of the positive charges does notchange during the process of charging.

It’s important to remember that the transfer of the charges fromone object to another is possible because the two objects arerubbing against each other. Both objects are neutral before theyare rubbed together. They become charged as a result of therubbing.

For any charging procedure, it’s important to keep in mindthat new electric charges are not being created. The electrons ineach object are just being rearranged within the object ortransferred to another object.


Figure 10.3 Amber is fossilized treeresin. This piece of amber containsbugs that were living on the tree andgot caught in the amber.

(a) (b)

neutral neutral negative positive

(c)

electrons

Figure 10.4 The amber and the fur are electrically neutral (a). If you rub the amber with thefur, electrons transfer from the fur to the amber (b). As a result, the fur becomes positivelycharged and the amber becomes negatively charged (c).

WORDS MATTER

“Electricity” comes from the Greekword elektron, meaning amber, whichis fossilized tree resin (Figure 10.3).Amber has been used for thousandsof years to study static electricity.

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Electron AffinityDifferent substances have differentabilities to hold on to electrons.The tendency of a substance tohold on to the electrons is calledelectron affinity.

Table 10.1 lists a series ofselected materials in order oftheir electron affinity. You willnotice that the higher the materialis in the list, the greater thetendency for that material to loseelectrons.

This means that if you rubtogether two materials listed inthe table, you can determinewhich material will be positivelycharged and which material willbe negatively charged. Forexample, if you rub nylon and steel together, the nylon willbecome positive and the steel will become negative. The nylonwill lose electrons, because it is higher in the table. Theelectrons from the nylon are transferred to the steel, making the steel negative.

This table is referred to as a “triboelectric” series. The termcomes from tribos, a Greek word meaning to rub.

Note that there can be a slightly different order for materialssuch as fur or wood depending on which type of animal the fur isfrom and which type of tree the wood is from.


Learning Checkpoint

1. Where are electrons in the atom?

2. What does “static” mean in “static electricity”?

3. What happens when two objects made out of different materials arerubbed together?

4. What term describes an atom’s tendency to hold on to electrons?

5. In each of the following pairs, state which one is more likely to give upelectrons.

(a) wood or human hair

(b) plastic wrap or steel

(c) cotton or silk

Suggested Activity •D3 Inquiry Activity on page 402

Tend to loseelectrons

Tend togain electrons

(+)

human hands (dry)

glass

human hair

nylon

cat fur

silk

cotton

steel

wood

amber

ebonite

plastic wrap

Teflon®

(–)

Table 10.1 A Triboelectric Series

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Laws of Attraction and RepulsionYou may have heard the expression “opposites attract” indiscussions about people. This is definitely true for electriccharges (Figure 10.5). Scientists studying the interaction ofobjects have observed that when a positively charged object isbrought close to a negatively charged object, the two objectsattract each other. When two objects with the same charge areplaced close together, the objects repel each other.

As a result of many scientific investigations, scientists haveestablished the following laws of static electric charges.

• The law of attraction states that particles with oppositecharges attract each other.

• The law of repulsion states that particles with like chargesrepel each other.

CoulombsCharles-Augustin de Coulomb was a French physicist whoworked with electric charges and made several importantdiscoveries (Figure 10.6). He showed that when two chargedobjects are placed closer together, the attraction or repulsionincreases. When the charged objects are moved farther apart,the attraction or repulsion decreases. In his honour, the metricunit for electric charge is named the coulomb (C). Onecoulomb equals 6.24 × 1018 electrons added to or removed froma neutral object.


Figure 10.6 Charles-Augustin deCoulomb (1736–1806)

Opposite charges attract.

Like charges repel.

Figure 10.5 If you increase the amount ofcharge on objects, the attraction orrepulsion also increases.

During Reading

Visualizing and Picture Mapping

Good readers use the strategy ofvisualizing to understand theimportant details of a largeamount of complex information.One way to visualize is to createa picture map. Using theinformation about the laws ofattraction and repulsion, begindrawing pictures to representthe information provided in thissection. Add to your picturemap as you read about electricalinsulators and conductors.

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Electrical Insulators and Conductors Another way to group materials is by their conductivity.Conductivity is the ability of materials to allow electrons tomove freely in them. Materials that hold onto their electrons anddo not allow them to move easily are called electrical insulators.An electrical insulator is a solid, liquid, or gas that resists orblocks the movement of electrons, as shown in Figure 10.7. Drywood, glass, and plastic are all examples of electrical insulators.An insulator can hold a static charge because static chargesremain nearly fixed in place.


Figure 10.7 Electrons in an insulator cannot move freely. Electrons in a conductor can.

Materials that allow electrons to change positions are calledconductors (Figure 10.8). Conduction is the movement ortransmission of electrons through a substance. Examples ofconductors include the metals copper and aluminum.

Some materials allow only some movement of electrons.This is the category of materials called fair conductors. In a fairconductor, the electrons do not move as freely as in aconductor, but they are not held almost in place as they are inan insulator.

(a) Insulator: The electrons (–) are boundtightly to the nuclei (+) so they resistmovement.

(b) Conductor: The electrons are not astightly bound to the nuclei. They can moveaway from the nuclei.

Figure 10.8 The metal wire in theelectric fence allows electrons tomove. The plastic insulator resists themovement of electrons.

+

+

+

-

--

+

++

---

+ -

+ +--

+-+-

+-+-

- -

--

-

- ---

++

+

++

+

++

++

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Table 10.2 gives some examples of conductors, fair conductors,and insulators. There are variations within each category, as somematerials are better or poorer conductors than others.

Water as a ConductorNotice in Table 10.2 that water is an insulator only if it is pure.However, most water has dissolved minerals in it, so itsconductive properties change and it becomes a fair conductor.This is why you do not want to be in a lake during athunderstorm. If lightning hits the water, the electric chargesfrom the lightning will spread out through the water and causeyou serious or fatal injury. This is also why you should not usewater to try to put out an electrical fire (Figure 10.9). You alsoneed to take care not to operate electrical appliances near wateror with wet hands.


Figure 10.9 Use an all-purpose fireextinguisher for an electrical fire.

Learning Checkpoint

1. (a) What does the law of attraction state?

(b) What does the law of repulsion state?

2. What is a coulomb?

3. Define “electrical insulator.”

4. What does “conduction” mean?

5. (a) Name two examples of good conductors.

(b) Name two examples of fair conductors.

(c) Name two examples of insulators.

Table 10.2 Conductivity of Selected Materials

Conductors Fair Conductors Insulators

copper water with dissolvedminerals

rubber

aluminum moist air wood

iron human body plastic

mercury carbon pure water

other metals soil metal oxides, such as rust

A Faraday cage is an enclosuremade of conducting material thatprotects its contents from electriccharges. Find out how airplanes,cars, and even some speciallydesigned clothes can act asFaraday cages. Start your researchat ScienceSource.

Take It Further

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D3 Inquiry Activity

QuestionWhat is the effect of charged objects on each otherand on neutral objects?

Procedure

1. Copy the following table into your notebook torecord your findings. Give your table a title.

2. Tape one end of a vinyl strip to the ring stand sothe strip hangs down. Rub the hanging vinyl stripwith the paper towel to charge it. Then, rub theother vinyl strip with the paper towel, and bringthat vinyl strip close to the suspended strip.Record your observations in your table.

3. Repeat step 2, using the two acetate strips andthe paper towel. Record your observations.

4. Bring one of the charged vinyl strips close to thesuspended acetate strip. Make sure the two stripsdo not touch each other. Record your observations.

5. Place the beaker upside down on the desk ortable. Place the watch glass on top of the beakeras shown in Figure 10.10. Balance the ruler so itis lying flat and centred on the watch glass. Bringa charged vinyl strip near, but not touching, oneend of the ruler. Record your observations.

6. Bring a charged acetate strip near one end of theruler. Record your observations.

Analyzing and Interpreting

7. Usually, charged vinyl is negative and chargedacetate is positive. How does this informationexplain your observations?

Skill Practice

8. Describe how you would modify the procedure inthis activity so that you could identify the type ofcharge on a charged object.

Forming Conclusions

9. Write three statements that summarize yourobservations.

Investigating Static Electricity

SKILLS YOU WILL USE� Adapting or extending

procedures� Drawing conclusions

• 2 vinyl strips


• ring stand

• paper towel

• 2 acetate strips

• beaker

• watch glass

• wooden ruler or metre stick

Materials & Equipment

Skills Reference 2

HangingObject

ApproachingObject Predictions Observations

chargedvinyl

chargedvinyl

chargedacetate

chargedacetate

chargedacetate

chargedvinyl

ruler chargedvinyl

ruler chargedacetate

Key ActivityDI

Figure 10.10 Balance the ruler on the watch glass on topof the beaker.

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Key Concept Review

1. (a) Draw a diagram of an atom that hasfour protons, five neutrons, and fourelectrons.

(b) Label each particle with its name andwhether it is positive (+), negative (–),or neutral.

2. (a) What is friction?

(b) Explain how friction can be used totransfer electrons. Use two substancesfrom the triboelectric series in Table10.1 on page 398 in your answer.

3. Explain why this statement is false: “Aneutral object contains no charge.”

4. State the two laws of static electric charges.

5. Where are static charges held?

6. Why might a plastic rod that contains alarge number of electrons not have a staticcharge?

7. (a) What is the difference between aconductor and an insulator?

(b) What is an example of a conductor?

(c) What is an example of an insulator?

8. (a) What is the difference between aconductor and a fair conductor?

(b) What is an example of a fair conductor?

9. Why can you not use water to put out anelectrical fire?

Connect Your Understanding10. Do two identical objects become statically

charged when you rub them together?Explain why they do or do not.

11. Copy this chart into your notebook. Foreach pair, predict which substance becomesmore positively charged and which becomesmore negatively charged when the twosubstances are rubbed together. Use Table 10.1, A Triboelectric Series on page 398, to help you make predictions.

12. Make a list of five different ways in whichyou experience static electricity in yourown life.

13. (a) While fishing in an aluminum boat inthe middle of a lake, you notice stormclouds forming nearby. Why is it a goodidea to get to shore as fast as possible?

(b) Would your answer change if the lakesomehow became filled with distilledwater with no ions present in it?Explain why or why not.

Reflection14. What are two questions about static

electricity that you would like to explorefurther?

For more questions, go to ScienceSource.


Pairs

Becomes MorePositivelyCharged

Becomes MoreNegativelyCharged

cotton, steel

cotton, silk

human hair,humanhands (dry)

Teflon®,wood

glass,plastic wrap

10.1 CHECK and REFLECT

Charged Pairs

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Charged Objects What does dust on a computer screen have in common withpaper on a comb (Figure 10.11)? In both examples, there isattraction between objects with unlike charges. You may havenoticed a similar effect when you unpack a box containingpolystyrene packing foam and the little pieces of foam stick toyour skin and clothes. Polystyrene is very low on the triboelectricseries and becomes charged very easily.

How do you know when an object is charged? Rather thantesting whether the object sticks to something else, you can usean electroscope, which is an instrument that can detect staticcharge. The electroscope was first invented in 1748 by a Frenchclergyman and physicist named Jean Nollet.

A metal-leaf electroscope has two very thin metal pieces,called leaves, suspended from a metal rod (Figure 10.12 on thenext page). The metal rod is attached to a top plate or metal knob.When a charge is transferred to the plate or knob, the chargesspread out over the whole structure, including the leaves. Thegreater the charge, the greater the separation between the leaves.

An electroscope is one of the devices that can be used to studystatic electricity. The study of static electric charges is calledelectrostatics.



• Electroscopes are instrumentsthat detect static charge.

• In charging by contact, anorginally neutral substancegains the same charge as thecharged object that touched it.

• In charging by induction, anoriginally neutral substancegains the opposite charge tothe charged object.

• Neutral objects are attracted tocharged objects.

• Grounding an object transferselectrons between the objectand the ground, making theobject neutral.

• An electrical discharge occurswhen charges are transferredquickly.

The Transfer of Static Electric Charges

Figure 10.11 The bits of paper are attracted to the statically charged comb.

10.2

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D4 Quick Lab

PurposeTo determine what happens to an electroscope whendifferent charged objects are brought near it

ProcedurePart 1 — Metal-Leaf Electroscope

1. Charge the comb or straw by running it throughyour hair, or rub an ebonite rod on a wool sweater.

2. Bring the charged object near, but not touching,the top of the electroscope (Figure 10.12).Observe the motion of the metal leaves. Then,move the object away and observe the leavesagain. Record your observations.

3. This time, touch the charged object to the top ofthe electroscope. You can rub the object alongthe top of the electroscope if necessary. Observethe motion of the metal leaves. Then, move theobject away and observe the leaves again.Record your observations.

4. Charge the glass, acrylic, or acetate rod byrubbing it with the silk fabric. Repeat steps 2and 3 using this charged rod.

Part 2 — Pith-Ball Electroscope

5. Charge the comb or straw by running it throughyour hair, or rub an ebonite rod on a woolsweater.

6. Bring the charged object near the pith ball butdo not touch it (Figure 10.13). Record yourobservations.

7. This time, touch the pith ball with the chargedobject. Then, touch it again. Record yourobservations.

8. Charge the glass, acrylic, or acetate rod byrubbing it with the silk fabric. Repeat steps 6and 7 using this charged rod.

Questions

9. What role did friction play in this activity?

10. With your group, explain what happened in Part1, using your knowledge about charges. Assumeyour object had a negative charge placed on it.

11. With your group, explain what happened in Part2, using your knowledge about charges. Assumeyour object had a negative charge placed on it.

Using an Electroscope

Figure 10.12 Metal-leaf electroscope Figure 10.13 Pith-ball electroscope

Materials & Equipment• plastic comb or straw or ebonite rod

• metal-leaf and/or pith-ball electroscope

• glass, acrylic, or acetate rod

• wool sweater

• silk fabric

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Detecting Static ChargeIn order to predict what charge is transferred to an electroscope,you can use a standard set of charged objects, such as ebonite andglass. Ebonite is a hard rubber material that is low on thetriboelectric series and readily accepts electrons. When ebonite isrubbed with fur, it becomes negative (Figure 10.14). Glass is highon the triboelectric series and tends to give away electrons. Whenglass is rubbed with silk or plastic, it becomes positive, as shown inFigure 10.14.

When a negatively charged rod is brought near a neutralelectroscope, the electrons in the electroscope are repelled by therod. The electrons move down into the leaves of the electroscope.The leaves are now both negatively charged, so they repel eachother and move apart (Figure 10.15). When the negativelycharged rod is taken away, the negative charges in theelectroscope are no longer repelled, so they move throughout theleaves, stem, and knob. The leaves drop down, and theelectroscope is neutral again.


Figure 10.14 To test unknown charges, you can use the known charges on an ebonite rod (a)and a glass rod (b).

+ ++ ++ + –– + + ––+ + ––

+ + ––

+ + ––

+ + ––+ + ––+ + ––

+ + ––

+ + ––+ + ––+ + ––+ + ––

+ +

––

+ + ––

+ + ––+ + ––

+ + ––

+ + ––

+ + ––

+ + ––+ + ––+ +

––

+ +

–––– ––

Figure 10.15 The leaves arenot separated in the neutralelectroscope (a). The leavesrepel each other when theyare charged negatively orpositively (b).

Suggested Activity •D5 Quick Lab on page 412

(a) (b)

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During ReadingCharging by Contact As you learned in section 10.1, electrons can be transferredthrough friction. Electrons can also be transferred throughcontact and conduction. You can charge a neutral object bycontact when you touch it with a charged object. Charging bycontact occurs when electrons transfer from the charged objectto the neutral object that it touches. The neutral object gains thesame type of charge as the object that touched it because theelectrons move from one object to the other (Figure 10.16).

InductionInduction is the movement of electrons within a substancecaused by a nearby charged object, without direct contactbetween the substance and the object.

If you rub a rubber balloon on your hair, electrons willtransfer from your hair to the balloon, making the balloonnegative. The charges stay in a nearly fixed, or static, position onthe balloon because rubber is an insulator. When you bring thenegatively charged balloon near a neutral wall, the negativelycharged electrons on the balloon repel the negative charges on thewall, making that part of the wall a positive surface. The balloonis said to induce a charge on the wall because it charges the wallwithout contacting it (Figure 10.17).


+ +

+ +

+ +

–––––––– ––––

+ + –– + + ––

+ ++ ++ +

(b) When a positively charged object touchesa neutral object, electrons move from theneutral object to the positive object and makethe neutral object positive.

+ ++ ++ +

––

––

––––

––+ + ––+ + ––

+ + ––+ + ––

+ + ––

Figure 10.16 (a) When a negativelycharged object touches a neutral object,electrons move to the neutral object,making it negative.

+ +

+ +

+ +

+ +

+ +

+ +

––

––

––

––

+ + –– + + ––+ + –– + + –––– + + ––

+ + ––+ + ––

+ + ––+ + ––

+ + ––

––

––

––––

––

––

––

––

––

+ + –– + + ––+ + –– + + ––

Figure 10.17 The negatively chargedballoon has induced a positive chargeon the wall’s surface without touchingthe wall.

Suggested Activities •• D6 Inquiry Activity on page 413• D7 Inquiry Activity on page 414

(a) (b)

Understanding Terms and Concepts

A Frayer quadrant can help youunderstand a term or theconcept it represents. Divide arectangle into four sections, andput the term or concept as therectangle’s title above it (e.g.,Charging by Contact). In the topleft section, write a definition ofthe term using your own wordsand words from the text. In thetop right section, write factsrelated to the term. In the lowerleft section, write examples ofthe term from the textbook. Inthe lower right section, writenon-examples of the term.

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Charging by InductionWhen you charge an object by induction, you use a charged object toinduce a charge in a neutral object and then ground the charged objectso it retains the charge. This newly charged object has the oppositecharge to the charge on the charging object. Grounding is the processof connecting a charged object to Earth’s surface. When you connect acharged object to the ground, you provide a path for charges to travelto or from the ground. Figures 10.18 and 10.19 show the process ofcharging by induction. Grounding occurs in diagram (b).


+ ++ +

+ +

+ + + +

electrons

+ ++ ++ + + ++ ++ +

+ + + +

+ +

+ + + + ––––

––

––––

–––– ––

–– –– –– –– –– –– –– ––

++––++––++––

++––++––

+ + –– + +

––

+ + ––

Figure 10.18

+++––––

––

––

––––

––

+ + + +

+ + + + + +

––––

––

–––––– ––

––

––

––

–– –– –– –– –– –––– ––

++––++––++––

++––

++––

++––++––++––

electrons

+ + –– + + ––+ + ––

+ + ––+ + ––

+ + ––

+ + ––

+ +

––

Figure 10.19

(a) When a negatively chargedobject comes near a neutralelectroscope, it repels theelectrons in the neutralelectroscope.

(b) When you ground the neutralelectroscope, you provide itselectrons with a path away fromthe repulsive influence. Someelectrons leave the electroscope.

(c) When you remove the groundand the charged object, theelectroscope is left with apositive charge because it haslost some electrons.

(a) When a positively chargedobject comes near a neutralelectroscope, it attracts electronsin the neutral electroscope.

(b) When you ground the neutralelectroscope, you provide a pathfor electrons to go toward thepositive influence.

(c) When you remove the groundand the charged object, theelectroscope is left with anegative charge because extraelectrons are trapped on it.

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Electrical DischargeOnce an object is charged, the charges are trapped on it until theyare given a path to escape. When electric charges are transferredvery quickly, the process is called an electrical discharge. Sparksare an example of electrical discharge (Figure 10.20).

Have you walked across a carpet and reached for a doorknobonly to be shocked when you created a spark (Figure 10.21)?When you shuffle your feet in slippers or socks on a carpet,electrons are transferred through friction and you build up astatic charge. When your hand reaches toward the neutraldoorknob, the excess electrons transfer due to induction.


Figure 10.20 When a sparkoccurs, the air becomes a passagefor the electrons to travel. Collisionsbetween moving electrons and airparticles release light and can alsomake a crackling sound.

Figure 10.21 When electrons jump between your hand and adoorknob, you can receive a surprising shock.

Learning Checkpoint

1. What does an electroscope detect?

2. In the contact method of charging, what charge does a neutral substancegain compared to the object that touched it?

3. In induction, what charge does a neutral substance gain compared to theobject brought near it?

4. What is the difference between charging by contact and charging byinduction in terms of electron transfer?

5. What is grounding?

9G10.42

Transfer of chargefrom girl to door

Transfer of chargefrom carpet to girl

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LightningLightning is an example of a very large electrical discharge causedby induction. In a thunderstorm, a charged area, usually negative,builds at the base of the cloud (Figure 10.22 (a)). The negativecharge at the base of the cloud creates a temporary positive areaon the ground through the induction process (Figure 10.22 (b)).When enough charge has built up, a path of charged particlesforms (Figure 10.22 (c)). The cloud then discharges its excesselectrons along the temporary path to the ground, creating a hugespark — lightning (Figure 10.22 (d)). This discharge creates arapid expansion of the air around it, causing the sound ofthunder.

It is interesting to note that air is normally an insulator. If itwere not, lightning would occur every time that clouds formed.For lighting to occur, charges in the clouds must build up to thepoint where the air cannot keep the charges separated from theground. At this point, the air stops being an insulator andbecomes a fair conductor, resulting in a lightning strike.

Earth is a donator or receiver of charge and is so large thatoverall it is not affected by the electron transfer of huge lightningstrikes. As a result, the ground is always considered neutral.


electrons

(a) (b) (c) (d)

electrons

Figure 10.22 Lightning is an atmospheric discharge of electricity.

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Sometimes, lightning strikes startfrom the ground and go to acloud. There are also cloud-to-cloud lightning strikes. Find outmore about different types oflightning. Create a visual display ofyour findings. Use ScienceSourceas a starting point.

Take It FurtherElectrostatic GeneratorsScientists use several devices in the laboratory to study how staticcharges create lightning and other phenomena, such as the staticthat affects clothes coming out of the dryer.

Early electrostatic generators were called “friction machines”because they used direct contact between different surfaces tocreate charged areas. A glass sphere or cylinder was rubbedmechanically by a pad to charge it up.

More recent machines, such as the Van de Graaff generator,create charge through friction between the roller and belt andthen transfer the charge to a large metal sphere, as shown inFigure 10.23.

A Wimshurst machine creates charges on two slowlyrotating disks with metal strips placed around the disks(Figure 10.24). The charge is built up using inductionbetween the front and back plates as the disks turn inopposite directions. The excess charge is collected bymetal combs with points near the turning disks.


charge collector

metal sphere

rubber belt

insulating support

comb

motor-drivenpulley

Teflon™ roller

nylon roller

Figure 10.23 (a) This Van de Graaff generator is set up so its domeis negatively charged. A Van de Graaff generator can also becharged positively by using different roller materials.

Figure 10.24 The Wimshurst machine uses induction to build up charge and create sparks.

Figure 10.23 (b) The static charge on a Van de Graaff generatorhas a hair-raising effect on these students.

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D5 Quick Lab

Materials that tend to lose electrons are higher on atriboelectric series. Materials that tend to gainelectrons are lower on a triboelectric series.

Purpose

To sort materials based on their ability to hold on tostatic charge

Procedure

1. Make a table like the one below to list yourmaterials, predictions, and results. Give yourchart a title. Record your predictions.

2.Record your predictions for what charge eachmaterial in each pair will have when thematerials are rubbed together.

3. Rub together the first pair of materials, A and B.Then, touch material A to the knob of theelectroscope to charge the electroscope.

4. Use a charged ebonite rod to test the charge onthe electroscope by bringing it near the knob. Do not touch the rod to the electroscope (Figure 10.25). Observe the motion of the leaves.

5. Record the charge of material A.

6. Ground the electroscope by touching it with your hand. Then, charge the electroscope using material B.

7. Use a charged ebonite rod to test the charge onthe electroscope by bringing it near the knob. Do not touch the rod to the electroscope.Observe the motion of the leaves.

8. Record the charge of material B.

9. Repeat steps 3–8 for each pair of materials.

Questions

10. Which materials were good electron receiversand would appear lower on a triboelectric series?

11. Which materials were good electron donors andwould appear higher on a triboelectric series?

12. Create a triboelectric series by listing thematerials you used in order, according to theirelectron affinity.

Charge Sorter

Materials & Equipment• materials such as fur, silk, aluminum, paper towel,

leather, wood, amber, hard rubber, Styrofoam®,plastic wrap, vinyl (PVC) and Teflon®

• metal-leaf electroscope

• known charged object, such as an ebonite rodrubbed on fur to create a negative charge

CAUTION: Some people are allergic to fur.

MaterialsPredictionof Charge

ActualCharge

A B A B A B

1. fur silk

2. fur aluminum

3. silk aluminum

4. silk paper

Figure 10.25 To test the charge on the electroscope, bring thecharged ebonite rod near it. Do not touch it.

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D6 Inquiry Activity

QuestionWhat charge does the electroscope gain compared tothe charging rod?

Procedure

1. Make a table like the following to record yourpredictions and observations. Give your table atitle. Record your predictions.

Trial A

2. Charge the ebonite rod by rubbing it with the fur.

3. Brush the ebonite rod against the top of theelectroscope. Record your observations of theelectroscope leaves using a labelled diagram.

4. Rub the ebonite rod with the fur again. Bring itnear, but not touching, the top of theelectroscope. Record your observations using alabelled diagram.

5. Charge the glass rod by rubbing it with silk. Bringthe glass rod near, but not touching, the top ofthe electroscope. Record your observations usinga labelled diagram.

6. Touch the top of the electroscope with your hand.

Trial B

7. Repeat steps 2–4 using a glass rod charged withsilk. Use a charged ebonite rod in steps 5. Repeatstep 6.

8. Return all materials to the areas designated byyour teacher.


9. (a) Explain why the leaves moved when theebonite rod touched the electroscope in step 3.

(b) What charge was left on the electroscope?

10. (a) Explain why the leaves moved when the glassrod touched the electroscope in step 5.

(b) What charge was left on the electroscope?

11. How do your predictions compare with yourobservations?

12. In terms of charge movement, explain in wordsand diagrams the effect of:

(a) an identically charged rod near the electroscope

(b) an oppositely charged rod near the electroscope

Skill Practice

13. Explain how you would find the charge of anunknown material.

Forming Conclusions

14. Write a summary statement about the charge theelectroscope gains and the charge of theinfluencing rod.

Charging by Contact

SKILLS YOU WILL USE� Making predictions� Observing, and recording

observations


• ebonite rod

• fur


• glass rod

• silk


Skills Reference 2

TrialMotion of Leaves

Predictions Observations

Trial A ebonite rodtouching

ebonite rodnear

glass rodnear

Trial B glass rodtouching

glass rodnear

ebonite rodnear

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D7 Inquiry Activity

Question What charge does the electroscope get compared tothe charging rod?

Procedure

1. Make a table like the following. Give your table atitle. Record your predictions.

Trial A

2. Charge the ebonite rod by rubbing it against thefur.

3. Bring the ebonite rod near the electroscope. Becareful not to touch the rod to the electroscope.While you hold the rod there, touch the top of theelectroscope with your hand.

4. Remove your hand from the electroscope, andthen move the ebonite rod away. Observe whathappens to the leaves of the electroscope.Record your observations.

5. Bring a charged ebonite rod near the electroscope.Record what happens to the electroscope leaves.

6. Bring a charged glass rod near the electroscope.Record what happens to the electroscope leaves.

Trial B

7. Repeat steps 2–5 except start by charging a glassrod against silk in step 2. Use a charged eboniterod for step 6.


8. (a) Compared to the original rod that was broughtnear the electroscope, what charge did theelectroscope end up with?

(b) How do you know?

9. Explain what happens to the electrons in theelectroscope when your hand touches theelectroscope.

10. (a) Why did you have to remove your hand firstbefore you moved the rod away?

(b) What would have happened if you had movedthe rod away and then your hand?

Skill Practice

11. How else could you ground the electroscope?

Forming Conclusions

12. Summarize the method of charging by inductionby using diagrams labelled with the motions ofcharges.

Charging by Induction

SKILLS YOU WILL USE� Gathering, organizing, and

recording relevant data frominquiries

� Interpreting data/information toidentify patterns or relationships

Skills Reference 2


• ebonite rod

• glass rod

• silk

• fur



TrialMotion of Leaves

Predictions Observations

Trial A ebonite rodaway

ebonite rodnear

glass rodnear

Trial B glass rodaway

glass rodnear

ebonite rodnear

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Key Concept Review

1. How are lightning and a spark similar?

2. (a) How do objects become negativelycharged using the contact method?

(b) How do objects become positivelycharged using the contact method?

3. Explain how a substance becomestemporarily charged by induction when acharged object is brought near.

4. Explain how to charge an objectpermanently using induction.

5. Using a sequence of labelled diagrams,explain how a positive balloon will stick toa neutral wall. Under each diagram,describe the motion of the charges.

Connect Your Understanding

6. (a) How does the process of groundingoccur when you receive a spark fromtouching a metal shopping cart?

(b) How does the process of groundingoccur during a lightning strike?

7. What would change about the way anelectroscope worked if its metal knob werereplaced with a plastic knob?

8. (a) Why do the leaves of the chargedelectroscope shown below move fartherapart if a rod with the same charge isbrought near?

(b) Why would the leaves move closertogether if the rod had the oppositecharge to the electroscope?

9. A person walks across a carpet, touches ametal doorknob, and receives a shock. If thesame person were carrying a metal rod, shewould not experience a shock whentouching the doorknob. Why?

10. Suppose a five-year-old child asks you toexplain why there is lightning. Write asimple explanation that you could sharewith the child. You may wish to include adiagram.

Reflection11. What are two things about static electricity

that you know now but you did not knowbefore you started this chapter?



+ + + + + +

+ + + + + + + +

metal knob


Question 8

Question 7

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Lightning Storm AwarenessOn a hot and humid summer night, lightning strikes a building inToronto (Figure 10.26). Along with the lightning, there wouldhave been loud claps of thunder. You may have noticed that as astorm moves closer, the time between lightning and thunderdecreases. This occurs because lightning travels very fast, at thespeed of light. Thunder travels much more slowly, at the speed ofsound. If you see lightning and hear thunder at the same time, thestorm is right above you.

Summer storms are common in Ontario and across Canada,but many people do not know what to do in these extremeweather conditions. Lightning storm safety begins by watchingfor towering cloud formations that signal developing storms.Lightning can strike up to 15 km from where it is raining. As aguideline, if you can hear thunder, you are in striking distanceand should look for shelter.

Safe shelter includes a large building because it will beproperly grounded if there is a strike. Cars, school buses, andother vehicles are also safe places, provided that the windowsare rolled up and you do not touch metal parts of the vehicle.



• Lightning rods are used toprevent damage to buildings.

• Grounding static charges can help prevent sparks nearflammable fuels.

• Paint sprayers work better ifthe object and the paint havedifferent charges.

• Photocopiers use electrostaticprinciples in their operation.

• Grounding wires preventdamage to electricalequipment.

• Electrostatic precipitators workby creating charged wasteparticles and usingelectrostatic attraction toremove the particles.

Electrostatics in Our Lives

Figure 10.26 Lightning can strike tall buildings repeatedly during a storm. The CN Tower(extreme right of photograph) is struck by lightning more than 70 times a year.

10.3

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If no safe shelters are available, you should avoid the highestpoint of land because lightning tends to hit these areas. Remainin a safe place for about 30 minutes after the last thunderclap.

A dangerous place to take shelter during a lightning storm isunder a tree, as the tree may be the highest point in the area. Thismakes it more likely to be struck by lightning. Also stay awayfrom objects that conduct electricity, such as bicycles,lawnmowers, and golf clubs. Summertime presents a higher riskof being struck by lightning both because there are more lightningstorms and because more people are outdoors participating inactivities such as baseball, swimming, fishing, and boating.

Lightning strikes cause about six deaths per year in Canadaand result in injuries to about 60 people. All of these could beprevented if everyone follows the few careful steps just describedas the storm approaches.


D8 Quick Lab

Lightning: Facts and Fiction

PurposeTo separate lightning facts from lightning fiction

Procedure

1. As a class, read the following true account of oneman’s close encounter with a lightning strike.Then, discuss the questions that follow.

Questions

2. What was his hair standing up an indication of?

3. (a) Holding a steel bar when the lightning struckwould almost certainly be lethal. Why?

(b) Would it make any difference if the steel barbeing held had one end in the ground whenlightning struck? Explain why or why not.

4. Describe the path the lightning may have takento result in blackened ground and a melted endof the steel bar.

5. What could the man have done differently inorder to be safer during the storm?

6. Describe how to keep safe if you find yourselfoutside during a thunderstorm.

7. If you find yourself out in the open during athunderstorm, you should crouch, keep your feetclose together, and stay on your toes.

(a) Why should you crouch on your toes?

(b) Why should you keep your feet close together?

STSE

A man was digging post holes in a large openfield. One of the tools he was using was a 2 msteel bar, which he used to pry rocks from theground. He was working in stormy weatherand wanted to finish a bit more work beforetaking cover.

Suddenly, he could feel the hairs on hisarms and legs begin to stand up. He threw thesteel bar as hard as he could and dove for theground. Then, he heard a deafening blast ofsound. The lightning strike missed him, and heran for cover.

Later, after the storm, he went back to thesite. The ground around the bar wasblackened, and one end of the bar appearedto have melted.

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Lightning RodsWhen lightning strikes a tree, the sap inside the tree conductsthe electricity down to the ground. In the process, the tree heatsup and expands very rapidly, resulting in an explosion and fire(Figure 10.27).

If the tree had been wet on the outside and dry on the inside,the electricity might have followed a different path to the groundand left the tree unharmed. Or if there had been a conductor, suchas a metal rod, that was slightly taller than the tree and that wasconnected to the ground, the lightning strike could have followedthe conductor safely to the ground and left the tree unharmed.

A lightning rod is a metal pole with a wire attached to it thatruns down to the ground. The main purpose of a lightning rod isto provide a point removed from the main structure of a buildingwhere a stream of electrically charged particles is more likely toform. The stream of electrically charged particles is highlyconductive, so if lightning strikes in the area around the building,it is much more likely to strike the lightning rod (Figure 10.28).This decreases the total amount of electric charge in the building,which makes it less likely to be struck by lightning. If lightninghits the lightning rod, the flow of electrically charged particles isdirected harmlessly down to the ground so the building is notdamaged, as shown in Figure 10.29.


Figure 10.27 A tree burned by lightning

Figure 10.28 The point on top of thisweather vane is a lightning rod.

lightningrod

ground rod

insulatedgroundingwire

Figure 10.29 The lightning rodredirects the electrical strike awayfrom the barn and harmlessly into theground.

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During ReadingGrounding Static Charges on VehiclesFriction occurs when two surfaces rub against each other. Thesurfaces may be solids, such as silk or glass, or they may be fluids,such as air or water. Automobiles and airplanes build up chargethrough friction between the vehicle’s outer surface and the air. Asimple way to prevent static build-up on a car is to use a groundstrap (Figure 10.30). However, dragging a strap along the groundwould not be a practical solution for airplanes.

Airplanes have needle-like projections located in variousplaces on the wings and plane body, as shown in Figure 10.31.The force of repulsion between charges becomes so strong arounda point that charges will disperse into the air from the point.


Figure 10.31 These needle-like rods on thewing of an airplane disperse static chargesinto the air.

Figure 10.30 Some drivers use agrounding strap to prevent static chargesfrom building up on their cars.

Figure 10.32 The nozzle and fuel truck must be groundedbefore refuelling an airplane begins.

Determining the Key Idea

Good readers synthesize detailsfrom a text to determine the keyidea. To do this, you makeconnections among the importantideas in the text, asking yourselfthe question “How does thisinformation connect to thatinformation?” As you read pages418 to 420, ask yourself how theinformation on one pageconnects to the information onanother page. What is the singlekey idea presented on thesepages?

Static Charges and Flammable MaterialsStatic charge build-up is particularly dangerous whenusing flammable materials (Figure 10.32). Whenairplanes are fuelled, the very explosive fuel movingthrough the nozzle creates a build-up of static charges.If the nozzle comes too close to the plane’s body, aspark could ignite the fuel. In order to prevent thisfrom occurring, the nozzle and fuel truck areconnected to the ground. Sparks are also dangerousnear the gas pumps at service stations. It is a good ideato ground yourself at a service station by touching ametal door handle before you slide across the seat toexit a vehicle.

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Reducing Static Charges in the HomeYou can use your knowledge of static charges to help youunderstand how to reduce charges. For example, static charges are built up when different types of insulators, such as nylon and polyester, rub together. This is why clothes made of differentmaterials often stick together when they come out of a clothesdryer (Figure 10.33).

More charges build up in dry air, such as during winter,because dry air acts as an insulator. Moist air is a fair conductor,so fewer charges build up on humid days. If you remove clothesfrom the dryer before they are completely dry, there will be fewercharges on them.

Sometimes, people add an antistatic dryer sheet to a clothesdryer. The dryer sheet adds a thin layer of waxy chemicals to thesurface of clothes so there is less friction between the surfacesand therefore fewer unlike charges to attract each other.

Sparks caused by static charges can damage sensitiveelectronic equipment. People who work with this type ofequipment take special care to reduce the risk of sparks. Forexample, carpets can cause static build-up.

Ways to reduce the risk of static sparks fromcarpets include:• using an antistatic mat for your feet• increasing the moisture in the air by using a

humidifier• spraying the carpet with antistatic spray• wearing an antistatic wrist strap

(Figure 10.34)• removing the carpet from the computer room


Figure 10.33 You can reduce thebuild-up of static charges by dryingonly the same types of materials atone time.

Figure 10.34 This computer technician wears an antistatic wrist strap toreduce the build-up of charges.

Learning Checkpoint

1. What is the function of a lightning rod?

2. How is charge build-up reduced on airplanes?

3. Why is a ground strap a necessary safety feature when transferring fuel?

4. What are three different methods for reducing charge build-up in clothesdryers?

5. What are four different methods for reducing charge build-up in acomputer room with a carpet?

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Making Use of Static ChargesStatic electricity can be a nuisance when it causes flyaway hair orsparks in your living room. It can be extremely dangerous when itoccurs near flammable materials or electronic equipment.However, static electricity can also be useful. Our ability tocontrol and direct static electricity has allowed us to designtechnological devices that make use of it to improve our lives.

Spray PaintingIf you have ever tried spray painting, you may have found it to be achallenging job. The paint comes out in a mist, and you lose a lotof paint because it doesn’t all land on the object you’re trying topaint. The paint comes out of the spray gun at a high speed, so thepaint particles bounce off the object being painted, wasting paint.

Electrostatics can help! Figure 10.35 shows a worker makinguse of electrostatics to paint a car. The paint coming out of thenozzle gains a negative charge through friction. The surface of thecar has been given a positive charge. Unlike charges attract, so thepaint is attracted to the surface of the car. There is less waste dueto bounce and overspray, and the finish is smooth and uniform.


Figure 10.35 Industrial sprayers such as those used to paint cars and boats take advantage ofthe laws of static charges.

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Laser printers make use ofelectrostatics in the printingprocess. Find out how a laserprinter works. Start your researchat ScienceSource.

Take It Further PhotocopyingThe word “photocopy” means to copy using light. Figure 10.36shows the typical steps involved in photocopying, including therole of electrostatics.


� �

��

� �

��

� �

��

� �

��

� �

��

Step 1A positive charge is created on the drum. The drum is an insulator, but it becomes a conductor when exposed to light. For this reason, it is called a photoconductor.

Step 2The image on the paper to be photocopied is projected onto the drum. Where the light hits the drum, the area becomes conductive, loses its charge, and becomes neutral. The dark areas remain positively charged.

Step 3Plastic particles and toner (ink) are sprayed onto the drum. As the particles come out of the sprayer, they get charged negatively. The negatively charged toner sticks to the positively charged areas on the drum, creating a copy of the original paper.

Step 4A sheet of paper is pressed against the drum and heated. Heat and pressure cause the toner to fuse to the paper. In some photocopiers, the paper is also charged to help the toner stick to it.

Step 5The paper is still charged and may be warm when it comes out of the photocopier.

��

��

��

lens

lightsource

page tobe copied

��

�

��

�

��

�

��

�

Figure 10.36 A model of a photocopying process


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Environmental ApplicationsAn electrostatic precipitator makes use of the laws of staticcharges to clean air (Figure 10.37). The gas discharged from afactory can contain tiny particles of pollutants, called particulatematter. One way to clean the gas before it is released is to send itthrough pipes that charge the particulate matter negatively. Thegas then moves through an area that has positively charged plates.The positive plates attract the negative particles and remove themfrom the gas. These collector plates are cleaned periodically tokeep the system running efficiently. Industrial plants thatproduce cement, steel, lumber, and petrochemicals use similartechniques to remove dust from the air.

We also use electrostatics in processes that purify and sortmaterials, such as ore separation in mining, plastics and paperrecycling, and the settlement of fine particles suspended in water.


grounding wire

conductors(metal plates)

clean gas out

ElectrostaticPrecipitator

solid waste collection

polluted gas in


D9

Advertisements for Static Control Products

If you have a problem with flyaway hair, clothessticking together in the dryer, or dust that will notstick to a mop, chances are there is a consumerproduct that has been designed to help you.

Discuss the following questions with your groupand record your answers.

1. Give examples of products that help consumerswith static control.

2. Are these products essential for everyday living?Why or why not?

3. (a) What do advertisers say about static in theirmessages to try to convince you to buy theirproducts? Is this information accurate?

(b) Do you think they are successful inconvincing people? Explain your answer.

Science, Technology, Society, and the EnvironmentSTSE

Figure 10.37 An electrostatic precipitator uses staticelectricity to remove particulates from gases in buildings orindustrial sites.

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D10 Quick Lab

Imagine painting your name on a piece of paperusing a paint that attracts electrons. Suppose youthen rubbed the paper with fur, causing your paintedname to gain a negative charge. You could sprinklecocoa or flour on the paper and the neutral cocoa orflour would be attracted to the charged paint. Thecocoa or flour would stick to your name, spelling itout in black or white. This is basically how aphotocopier works. In this activity, you will investigatea variation of this technique.

PurposeTo investigate the principles of photocopying

Procedure

1. Cut a paper circle the size of the petri dish.

2. Turn the paper into a stencil by cutting out asimple symbol such as a diamond or your initial.

3. Add cocoa or flour to the dish. Jiggle the dish inorder to spread the cocoa or flour evenly.

4. Using a minimum of tape, attach the edge of thecircle to the outside of the lid.

5. Using the wool cloth, gently rub the lid areashowing through the paper for about a minute,as shown in Figure 10.38.

6. Carefully remove the stencil. Put the lid on thedish.

7. Turn the dish upside down while holding the lid.Then, turn it right side up.

8. Remove the lid. Record your observations.

Questions

9. What did you observe in step 8?

10. How would you explain your observations?

Make Your Own Photocopier


Figure 10.38 Rub the lid gently.• paper and scissors

• plastic petri dish andlid


• cocoa or flour

• wool cloth


CAUTION: Never eat anything in science class.

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D11 Quick Lab

An electrostatic precipitator uses static charges to separate particles in order to purify and sort materials.

PurposeTo study how an electrostatic precipitator works

Procedure

1. Lay a long piece of paper towel on a table.Sprinkle pepper, flour, salt, and bits of lint on thepaper towel.

2. Inflate and tie off three balloons. Charge theballoons by rubbing them against your hair or asweater. Hold the balloons above the table butnot directly above or touching the paper towel.

3. Have a partner pull the paper towel across thetable slowly under the balloons (Figure 10.39).Observe which materials are taken up and howmuch of the material is left.

4. Clean the balloons and recharge them. Repeatstep 3 with the remaining particles on the towel.

5. Clean up your work area. Wash your handsthoroughly.

Questions

6. (a) Which particles were the easiest to pick up?

(b) Which particles were difficult to pick up?Explain why.

7. What happened to the ability of the balloons topick up particles as time went on?

8. Why do you think this method is used to removeparticulate matter from the air?

9. What factors would affect the efficiency of a precipitator?

Make Your Own Precipitator

Figure 10.39 Pull the paper towel across the table slowly.

Materials & Equipment• paper towels

• ground pepper

• flour

• salt

• lint

• 3 balloons

CAUTION: Never eat anything in science class.

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Key Concept Review

1. Why is it not a good idea to take shelterunder a tree in a thunderstorm?

2. (a) What are the three parts of a lightningprotection system for a building?

(b) What is the function of each part?

3. What causes the static build-up on movingvehicles such as cars and airplanes?

4. Large trucks that carry flammable liquidsoften have a metal wire or chain that dragson the ground. Why?

5. Sometimes, finished photocopied paper willstick to you. Explain why.

6. Name four applications that useelectrostatic principles.

Connect Your Understanding 7. Why does Earth not become charged when

many people in the world ground objects?

8. How can neutral pollutant particles bemade attractive to the charged plate in anelectrostatic precipitator?

9. The technician in this photo is using a toolthat has insulated handles. Why is thisimportant for working on electronicequipment?

10. When spray paint is applied to a car, thepaint has a negative charge and the surfaceof the car has a positive charge. Someprocesses use a negatively charged paintand a grounded object. Explain why thisalso works.

11. Flowing fluids, such as water, oil, and air,produce static charge. Why is it not asimportant to create static charge safetyrules for handling flowing water as forhandling air or oil?

12. Suppose you have a static charge problem athome. Your clothes stick to your body, thereare socks stuck to your sweater from thedryer, and you always get a shock fromtouching a doorknob after walking acrossyour carpet. Suggest ways you can reduceor eliminate these and similar problems.

13. Explain the importance of protectingcomputer equipment from static discharge.

14. Explain how eliminating static electricitywould hinder the performance of a spraypainting device.

15. Suppose a building had a lightning rod thatwas not connected to a ground rod by aconducting wire. Would this set up stillprovide protection from lightning strikes?Explain.

Reflection

16. Which device that makes use of staticelectricity has the greatest effect on yourlife? Why?




Question 9

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SCIENCEeverywhereeverywhere

Deep BrainStimulationDeep BrainStimulation

This X-ray shows how deeply the twoelectrodes are placed inside the brain. Theelectric signals are generated by a smalldevice implanted in the patient’s chest,near the shoulder. The electric circuits areprogrammed using a computer thatcontacts the device using radio signals. Thismeans the electric impulses can beadjusted with the device implanted in thepatient’s body. Using special magnets,patients or their doctor can even turn thedeep brain stimulator on or off.

This device is sometimes called a“pacemaker for the brain.” A pacemaker isan implanted device that supplies electricsignals to the heart to help it beat regularly.A brain pacemaker causes deep brainstimulation. It stimulates the brain bysending electric impulses to target areasdeep within the brain. These electricimpulses interfere with naturally occurringelectric impulses in the brain that causeuncontrolled shaking, called tremors, in apatient. Tremors are a symptom of severalconditions, including Parkinson’s disease.Tremors can prevent people from walking,feeding themselves, or even just being ableto sit still.

Before receiving the deep brain-stimulatingdevice, this patient was unable to control his

arms and was unable to speak clearly. With hisnew implants sending electric signals to his brain,

he is able to use his steady hand to enjoy a hot cup ofcoffee without worrying about spilling it and burning himself.

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Key Concept Review1. (a) What are the possible interactions

between two charged objects?

(b) How do a charged object and a neutralobject interact?

2. Explain the role of friction in creating acharged object.

3. (a) Two neutral objects, A and B, wererubbed together, resulting in object Abeing charged positively. What is nowthe charge on B?

(b) How do you know?

(c) Which object, A or B, is likely higher onthe triboelectric series?

(d) How do you know?

4. For the following three electroscopes,explain which way the leaves will movewhen a charged rod is brought near.Explain your reasoning.

5. (a) Describe how to leave an objectpositively charged using the inductionmethod.

(b) Describe how to leave an object negativelycharged using the induction method.

6. How would you ground an electroscope?

7. (a) Define electrical discharge.

(b) What is a real-life example of anelectrical discharge?

8. Describe a device that uses static electriccharges. Include a labelled diagram as partof your answer.

9. Describe a device that protects other devicesby controlling static electric charges. Includea labelled diagram as part of your answer.

Connect Your Understanding10. Explain why a positively charged balloon

will stick to a wall just as easily as anegatively charged balloon.

11. Would the humidity (moisture content) ofthe air make a difference in thephotocopying process? Explain. t

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ACHIEVEMENT CHART CATEGORIES

Knowledge and understanding Thinking and investigaion

Communication Applicationac

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10 CHAPTER REVIEW

UNIT D The Characteristics of Electricity

Question 4

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12. Suppose you had a plastic lightning rod thatwas the same size and design as a metallightning rod. Would the plastic lightningrod work better than, the same as, or not aswell as a metal lightning rod? Explain youranswer.

13. Would a negatively charged balloon stick toa metal wall as easily as to a wooden wall?Explain why it would or would not.

14. You have an unknown material thatbecomes charged when you rub it with silk.You also have a negative ebonite rod and apositive glass rod. How can you determinethe charge of the unknown object?

15. If lightning hits a car, the effect is minimal.Explain why.

16. Two identical objects are both chargedpositively, but one object has about twice asmuch positive charge as the other object.What would happen to the charges whenthe two objects are brought together?Explain your answer.

17. (a) How would using a humidifier in ahome affect static charge build-up?

(b) Would you need to use a humidifiermore in the summer or the winter?Explain.

18. Explain two different actions that couldcause static charges to build up on acomputer.

19. If you wrap plastic wrap on a glass bowl,the plastic wrap will cling to the bowl. Useyour understanding of static charge toexplain why.

20. You run a brush through your hair andwonder if it has become statically charged.Design a test that allows you to determine ifthe brush has a charge.

21. What materials could be woven into apolyester carpet to prevent a static chargefrom building up on a person walkingacross the carpet? Explain the reasons foryour choice.

Reflection

22. What information from this chaptersurprised you or was not what youexpected? Explain why.

23. (a) How would you rate your participationin the labs you did in this chapter?

(b) How could you improve yourparticipation? c

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Reflect and Evaluate

Revisit the key learning goals that you set in theBefore Reading activity at the start of this chapter.How did the During Reading strategies help you toaccomplish your goals? Write a paragraph thatsummarizes how the reading strategies assistedyour learning. Compare your paragraph with apartner’s. Add any new insights you gained fromreading your partner’s reflection.

After Reading

Unit Task Link

Storing large amounts of electricity is very difficult.This means that electricity is usually generated asit is being used. Generating facilities increase anddecrease the amount of electricity they producedepending on how much electricity thecommunity is using at any given time. Explain howan electrical grid connecting many differentelectrical generating sources and severalcommunities provides a dependable source ofelectricity. Brainstorm a list of different ways ofgenerating electricity. Sort them from mostimportant to least important. Share your ideas withyour class.

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