10.3 Electrostatics in Our Lives - Kwic Internetmy.kwic.com/~gpguch/files/9chapter10.3.pdf · 2018-04-05 · and should look for shelter. Safe shelter includes a large building because

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.

416 UNIT D The Characteristics of Electricity

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

• 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.

417Static charges collect on surfaces and remain there until given a path to escape.

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.


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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.

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lightsource

page tobe copied

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Figure 10.36 A model of a photocopying process

Suggested Activity •D10 Quick Lab on page 424

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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

Suggested Activity •D11 Quick Lab on page 425

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

• clear adhesive tape

• cocoa or flour

• wool cloth

Materials & Equipment

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?

For more questions, go to ScienceSource.

10.3 CHECK and REFLECT


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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10.3 Electrostatics in Our Lives - Kwic Internetmy.kwic.com/~gpguch/files/9chapter10.3.pdf · 2018-04-05 · and should look for shelter. Safe shelter includes a large building because