1. The Characteristics of Electricity
UNIT 4
The Characteristics of Electricity
Chapter 10: Static Charges and Electricity
Chapter 11: Electric Circuits
Chapter 12: Generating and Using Electricity

2. Static Charges and Electricity
CHAPTER 10
In this chapter, you will:
relate your understanding of the atom to the study of electricity and static charges
explain the characteristics of conductors and insulators, and learn how different materials allow static charges to be collected or discharged
apply your understanding of electrostatics to describe technologies that control or use electricity
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3. Lightning in a Glow Tube
(Page 401)
How can you use common materials to generate an electric charge that will light up a glow tube?
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4. 10.1 Exploring Static Charges
(Page 403)
Electricity is a form of energy that results from the interaction of charged particles such as electrons or protons.
Static charge (static electricity) is an electric charge that tends to stay on the surface of an object rather than flowing away quickly. Static charges build up when different materials rub together. The process of charging materials by rubbing them together is called charging by friction.
Clothes in a dryer build up a static charge when they rub together and are charged by friction.
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5. The Bohr –Rutherford Model of the Atom
(Page 404)
The Bohr-Rutherford model of the atom has a nucleus that contains positively charged protons and neutral neutrons. Negatively charged electrons lie outside the nucleus.
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6. Causes of Electric Charges
(Page 404)
In the image below, electrons are transferred from the hair to the comb. The hair is left with an excess of protons (or a shortage of electrons) resulting in a positive charge, and the comb is left with an excess of electrons, resulting in a negative charge.
Only electrons are transferred between the hair and comb. Protons and neutrons cannot leave the nuclei they reside in.
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7. An Electrostatic Series
(Page 405)
The electrostatic series (triboelectric series) is a list of materials arranged according to their ability to hold onto electrons. When a material higher on the list is rubbed with a material lower on the list, it loses electrons and becomes positively charged. The material that gained the electrons becomes negatively charged.
If two items far apart on the series are rubbed together, you can accurately predict their resulting charges.
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8. Anti-Static Sheets
(Page 406)
Static cling develops among clothes in a dryer because the different fabrics either lose or gain electrons as they rub against each other. Anti-static sheets coat the clothes with a waxy material that makes them behave like they were all made of the same material, effectively preventing static cling.
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9. Insulators and Conductors
(Page 406)
Insulators are materials in which electrons cannot move easily from atom to atom. Examples include glass, rubber, plastic, cotton, wool, nylon, and pure water.
Conductors are materials in which electrons can move easily from atom to atom. Examples include metals (copper, aluminum, gold, silver), and solutions containing water (e.g., salt water, tap water)
Semi-conductors are materials that conduct electricity fairly well under certain conditions. Examples include silicon, germanium, and gallium.
The conductivity of a material can be tested by connecting it to a conductivity meter/tester. When the contact points touch the material, if the electrons flow, a light will go on.
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10. Reviewing Insulators and Conductors
Click the “Start” button to review conductors and insulators.
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11. Grounding: Removing Static Charges
(Page 407)
The simplest way to remove the net static charge in an object is to put it in contact with what is called a ground. A ground is an object that can neutralize a charged object by either supplying or removing a very large number of electrons. This neutralizing is called grounding. In this process, the ground remains neutral.
Ground symbol
While Earth itself is only a fair conductor, it does have an enormous capacity to absorb or supply electrons while remaining neutral. For this reason conductors are often grounded to Earth.
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12. Shocking Results
(Page 408)
You feel a shock when a relatively large number of electrons flow rapidly through your hand. People receive a small shock when they walk in stocking feet on carpet and then touch a metal doorknob. The excess electrons in the person’s body are discharged into the conducting metal doorknob. If the person’s body has a positive charge, electrons will move from the doorknob into the person’s hand.
If some of the excess electrons are removed by touching the wooden door first, then the charge is slowly reduced and a shock is not felt.
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13. Static Discharge and Electronics
(Page 409)
Electrical equipment can be seriously damaged by static charges. Computer hard drives can lose data and circuit boards can be damaged if electrons are discharged into them. For this reason, measures such as grounding and the wearing of anti-static clothing (coats, gloves, and hair covers) must be taken when working around electronics.
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14. Grounded for Good
(Page 409)
Static electricity can be generated by friction in many ways. To avoid dangerous situations, precautions must be taken to reduce the build-up of charges.
Sparks from electrostatic discharge have resulted in explosions in grain elevators, flour mills, coal mines, gasoline tanks, and down in sewers.
Grounded Fuel Truck
Electrostatic build-up is reduced by grounding objects to release charges, by having people wear anti-static clothing, by coating surfaces with anti-static paints or coatings, by keeping the humidity of static-prone workplaces high, and through the use of ionizers (devices that produce neutralizing charges).
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15. Concepts to be reviewed:
Section Review
(Page 410)
Concepts to be reviewed:
What is a static charge? How does it behave?
What causes static charges to build up in an object?
How are subatomic particles (protons and electrons) related to static charge?
How are charges transferred from one object to another? Why are they transferred?
How do materials in an electrostatic series behave with respect to the transfer of charges?
What is the difference between insulators, conductors, and semi-conductors?
How and why can grounding be used to remove charges?
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16. 10.2 Charging by Contact and Induction
(Page 411)
The presence of electric charges can be detected using a simple device called an electroscope.
Most electroscopes indicate that a charge is present by having either a component that moves to one side or the other or components that move apart.
In the example in the large photo on the left, the two metal leaves move apart when the charged object is touched to the electroscope. In the small image, a small ball is moving away from a charged object.
Copyright © 2010 McGraw-Hill Ryerson Ltd.

17. Charging by Contact
(Pages 412-3)
Charging by contact involves generating a charge on a neutral object by touching it with a charged object. The image below illustrates how charges are transferred through contact.
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18. The Laws of Electric Charges
(Page 413)
The laws of electric charges describe how two objects interact electrically when one or both are charged. These laws can be used to predict the behaviour between charged and/or uncharged objects.
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19. The Amount and Type of Charge
(Page 414)
The amount and type of charge on an object depends on the difference between the number of protons and electrons it contains. An electric field is the space around a charged object, where the effect of the charge can be felt by other objects.
The size of the electric force between two charged objects is directly proportional to the amount of charge on each object, regardless of whether the force is an attraction or a repulsion.
If an object is charged, it must demonstrate repulsion between it and another object.
The laws of charges can be used to determine the type of charge.
If an object of unknown charge is attracted to both positive and negative charges, it is neutral.
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20. Charging By induction
(Page 415)
When a charged object is close to a neutral object, its electric field produces a force on the neutral object. The charged object causes the electrons in the neutral object to move. This movement of charges can result in portions of the neutral object developing a negative charge, and other areas developing a positive charge. + - - + + - - + + - - +
Induced charge separation is the movement of electrons in a substance, caused by the electric field of a nearby charged object, without direct contact between the substance and the object.
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21. Concepts to be reviewed:
Section Review
(Page 417)
Concepts to be reviewed:
What is an electroscope? How can one be used to detect the presence of an electric charge?
What are the three laws of electric charges? How can they be used?
What type of charge results in an object charged by contact?
How is the electric force between two objects transmitted?
What is an induced charge separation? How is one produced?
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22. Charges at Work
(Page 418)
Electric charges are used in many applications. These include controlling pollution, reducing waste, making copies of documents, painting vehicles, monitoring workers’ safety, and studying subatomic particles.
Credit: Wikipedia
Copyright © 2010 McGraw-Hill Ryerson Ltd.

23. Lightning
(Page 418)
A lightning bolt is an example of a gigantic electrical discharge. Moderate thunderstorms generate as much energy as a small nuclear generating plant.
Storm clouds contain a complicated mix of raindrops, ice particles and air. As these materials swirl around within the cloud, charges are transferred and ions (charged atoms or groups of atoms) are formed.
Lightning bolts represent the instantaneous discharge of the charges that have built up within a cloud. The lightning bolt generally hits the highest object in an area.
Copyright © 2010 McGraw-Hill Ryerson Ltd.

24. Lightning
(Page 419)
The steps involved in producing a lightning bolt are illustrated in the next two slides.
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25. Lightning
(Page 419)
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26. Click the “Start” button to review the formation of lightning.
Reviewing Lightning
Click the “Start” button to review the formation of lightning.
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27. Lightning Rods and Safety
(Page 421)
Lightning rods are metal spheres that are connected to the ground with a thick insulated metal cable. Lightning rods reduce the likelihood of a lightning strike and safely conduct the charge to the ground if a strike does occur.
Lightning rods are particularly important in rural areas where a house or barn may be the tallest structure. Lightning strikes can set structures on fire, and they cause about one third of all forest fires.
In Canada, most lightning storms occur in June, July, and August.
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28. Using an Electric Charge to Reduce Pollution and Waste
(Pages 421-2)
Electrostatic precipitators (ESPs) are a type of air cleaner that removes unwanted particles and liquid droplets from a flow of gas (exhaust fumes). ESPs are very effective for reducing pollution from smokestacks.
Dust and droplet particles are positively charged by a wire in the precipitator. The charged particles are then collected on a negatively charged plate, where they are neutralized and then collected in hoppers.
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29. Electrostatic Spray Painting
(Page 423)
When using an electrostatic sprayer to apply paint to objects, the paint or powder is given a charge as it leaves the nozzle of the sprayer. The object to be coated is either grounded or given a charge opposite to that of the paint. The paint particles are then attracted to the surface being coated, which minimizes the amount of over-spray and produces a smooth, even coat of paint.
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30. E-waste
(Pages 422-3)
E-waste is waste resulting from the discard of electronic materials that we no longer consider to be useful. The electronic products can contain heavy metals such as mercury, lead, and cadmium that can easily leach into ground water if disposed of incorrectly.
Most e-waste can be recycled, but little is because of the costs involved. Safe recycling methods are expensive, so much of the waste is exported to developing countries where less environmentally friendly recycling methods are practiced.
Extended Producer Responsibility policies make companies responsible for their products when consumers are through with them.
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31. The Van de Graaff Generator
(Page 424)
Van de Graaff generators are devices that accumulate very large charges. These devices are used in classrooms to illustrate electrostatic charges. They have also been used to test electronics, and larger versions have been used in atom-smashing devices since the 1930s.
A rubber belt inside the generator is charged by friction as it moves around two rollers. The charge is transferred to a metal comb attached to the sphere, where it builds up.
The charge is then transferred to anyone who touches the sphere, with hair-raising results.
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32. Photocopiers, Laser Printers, and Scanners
(Page 425)
A photocopier, laser printer, or scanner makes an electrostatic image on an aluminum drum coated with selenium (a metal whose conductivity changes with the amount of light it receives). Parts of the drum hit by light become neutrally charged, while parts receiving no light become positively charged. Toner is attracted to the positively charged parts of the metal drum and eventually forms a dark image on a sheet of paper.
The paper is given a greater charge than the drum so the toner sticks to it.
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33. Radiation Dosimeters
(Page 427)
Over-exposure to radiation can be very hazardous to a person’s health and general well-being. People who work with radioactive materials or are exposed to other sources of radiation on a regular basis need to be aware of the amount of exposure they have received. Dosimeters help monitor radiation exposure.
A radiation dosimeter detects and measures exposure to radiation. Radiation exposure causes a gas within the dosimeter to become a conductor. A fibre within a dosimeter acts like the leaves in an electroscope and changes position related to the amount of radiation a person has been exposed to.
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34. Concepts to be reviewed:
Section Review
(Page 428)
Concepts to be reviewed:
What is a lightning rod? How can it be used to protect people from electrostatic discharge?
How do electrostatic precipitators remove pollutants from smokestack gas flows?
How can particles that have different masses be separated using electrostatics?
How do Van de Graaff generators produce large charges?
What role do static charges play in the functioning of a photocopier?
What is a dosimeter? How do static charges help it to function?
Copyright © 2010 McGraw-Hill Ryerson Ltd.