nelson science connections 9 teacher resource draft material

Nelson Science Connections 9 Teacher Resource DRAFT Material

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Chapter 12 Static and Current Electricity Key Question: What is electricity?

Key Concepts Vocabulary

Electricity describes how electrons move from one place to another.

Static electricity is the result of an imbalance of charges on the surface of an object.

There are many useful applications of static electricity.

Objects can be charged by contact or by induction.

Current electricity is generated by moving electrons in a closed path. Some materials allow electrons to move through them easily (conductors), while others do not let electrons move through them easily (insulators).

electric force electric charge neutral neutral object negatively charged object positively charged object Law of Electric Charges static electricity electric discharges charging by friction

charging by conduction induced charge separation charging by induction grounding conductor insulator conductivity electric current direct current (DC) alternating current (AC)

TEACHING NOTES • Have students look at the chapter opener photo on page 456 of the Student

Book. – Ask, What is happening in the picture? (Lightning is striking the CN

Tower.) Why do you think it is striking the tower rather than the other buildings? (The CN Tower is the tallest structure in the area.)

– Ask, Why do you think lightning often occurs during a thunderstorm? (Sample answer: Something is happening in the clouds to produce electricity.)

– Ask, Why do you think lightning is so dangerous? (Sample answer: It is a sudden release of a tremendous amount of electrical energy.)

• Have students describe situations in which they have seen lightning. Encourage them to describe what they saw, what they heard, and the weather conditions at the time.

Engage the Learner

Chapter Introduction • To preview the major ideas that will be explored in the chapter, review the

Key Concepts. Ask a student volunteer to read each Key Concept aloud before it is discussed. Ask prompting questions to assess students’ prior knowledge and to engage students in the topics. Examples are given:

1. What are electrons? (Electrons are negatively charged particles.) 2. What do you think an imbalance of charges means? (There is a greater

charge in one area than in another area.)


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3. How could the static electricity of charged objects be used? (Sample answer: Photocopiers rely on static electricity.)

4. Describe a time when you have experienced an electric charge. (Sample answer: I was shocked when I walked across a carpet and touched metal.)

5. How do you think electricity in the wires of your house is different from a shock you get after walking across a carpet? (Sample answer: Electricity in a house is a continuous flow.)

6. Why do you think electrical wires are covered in rubber? (Electricity cannot easily flow through rubber.)

Engage in Science • The inset photo on page 457 of the Student Book shows the world’s largest

van de Graaff generator, which is located at the Museum of Science in Boston, Massachusetts. The person in the cage is protected because the electric charges repel each other and spread out over the surface of the cage. This demonstrates how people inside an airplane or a car are protected when lightning strikes it.

What Do You Think? • Together with students, consider each photo and statement in the

anticipation guide on page 458 of the Student Book. Below are some sample questions you can use to elicit students’ previous knowledge and experience. Encourage students to express their opinions, acknowledging that their opinions may change as they read through the chapter.

1. What type of electricity is used in homes? 2. How do you think photocopiers get the ink to stay on paper? 3. What would cause the strands of hair as shown in the photo to separate? 4. Why is the water attracted to the comb? 5. Would water move through a pipe if there were no push to make it flow? 6. How could we use static electricity to our benefit? • Poll the class on whether they agree or disagree with each statement.

Revisit the poll results at the end of the chapter in the What Do You Think Now? section.

Focus on Reading Evaluating

• Use the excerpted passage in this feature to illustrate how to evaluate a text. Explain that the opinion or judgement made while evaluating a passage does not have to be a value judgement. Demonstrate this by pointing out the sample evaluation: it does not say that the passage is good or bad. It simply describes the student’s understanding after reading the passage.

• Review with students the difference between an evaluation and a summary. A summary restates the content of a passage in a concise way. An evaluation may include a summary, but also includes a judgement or opinion.


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• Distribute BLM 0.0-11 Reading Strategies Checklist to help students improve their reading skills.


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DIFFERENTIATED INSTRUCTION • Allow interpersonal learners to discuss the statements in What Do You

Think? with a partner before agreeing or disagreeing. • You may want to have students who are interested in computers set up a class

blog, wiki, or website for posting reports, lab results, presentations, images, videos, links, and other forms of information.

LITERACY TIPS AND ENGLISH LANGUAGE LEARNERS • The concept of charge is fundamental to understanding this chapter. Review

with students the multiple meanings of the word charge. Ask them to write a sentence illustrating each meaning and to identify the meaning (or meanings) most likely to be used in this chapter.

Related Resources Fujitaki, Kazuhiro. The Manga Guide to Electricity. No Starch Press, 2009. Science Connections 9 ExamView® Test Bank Science Connections 9 Teacher eSource SUITE Upgrade Science Connections 9 website www.nelson.com/scienceconnections/9


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12.1 Electric Charges

OVERALL EXPECTATIONS: A1, E2, E3

SPECIFIC EXPECTATIONS

Scientific Investigation Skills: A1.1, A1.5, A1.10, A1.11

Developing Skills of Investigation and Communication: E2.1, E2.3

Understanding Basic Concepts: E3.2 The full Overall and Specific Expectations are listed on pages xx–xx.

KEY CONCEPTS • Static electricity is the result of an imbalance of charges on the surface of an

object.

• Objects can be charged by contact or by induction.

EVIDENCE OF LEARNING Look for evidence that students can

• describe how negatively and positively charged objects affect each other

• identify and describe the three main particles that make up an atom

• explain how a neutral object can become negatively or positively charged

• relate the electric force to the strength of an electric charge and the distance between objects

SCIENCE BACKGROUND

What Holds a Nucleus Together? • The nucleus of an atom consists of

positively charged protons and neutral neutrons. A common question, then, is Why don’t the protons repel each other, causing the nucleus to fly apart? The answer is that the protons do repel each other. However, another force is present at very small distances. This strong force is an attractive force between protons and neutrons in the nucleus. Because that force is about 100 times stronger than the electromagnetic force, the nucleus stays together despite the force of the protons repelling each other.

Coulomb’s Law • The force between two electric charges

can be described mathematically by Coulomb’s Law:

2BA

rqqF ∝

The law states that the electric force (F) is proportional to the magnitude of the charges ( ) and is inversely proportional to the square of the distance between the charges (r

BAqq2). If one of the

charges doubles, the force also doubles. If the distance between the charges doubles, the strength of the force decreases to one-fourth of the previous amount.


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POSSIBLE MISCONCEPTIONS – Identify: Students may think that the moving charges that create the

electricity flowing through wires can be either electrons or protons. – Clarify: The moving charge in static or current electricity in a solid

conductor is always an electron. – Ask What They Think Now: At the end of the lesson ask, Which type of particle

carries electric charge through wires? (An electron carries electric charge.)

TEACHING NOTES

Engage

• Organize the class into small groups. Provide each group with a plastic spoon or ruler, bits of tissue paper, and a piece of wool. Have students take turns rubbing the spoon or ruler with wool and then using it to attract bits of the paper. Ask students to describe what they think causes the attraction.

Explore and Explain

• Ask students to identify the name and charge of each type of particle in Figure 1. Remind them that an atom’s identity depends on the number of protons. If the atom in Figure 1 had a different number of protons, it would no longer be lithium. Ask, Which particles do you think can be most easily removed from an atom? Why? (Electrons can be most easily removed because they are not bound in the nucleus.)

• Have students study Figure 2 on page 460 of the Student Book. Point out that because all objects are made of atoms, all objects contain positive and negative charges. Ask, What is true about the charges of a neutral object? (The positive charge equals the negative charge.) What is true about a positively or negatively charged object? (The number of positive and negative charges is unbalanced.)

• Draw a model aluminum atom on the board, similar to the drawing in Figure 1, but with 13 protons, 13 electrons, and 14 neutrons. Tell students that this represents the atoms that make up the spheres shown in Figure 2 on page 461 of the Student Book. Ask a volunteer to come to the board and change the atom so that it has a positive charge. The student should erase an electron. Have another volunteer draw the model so it has a negative charge. The student should add electrons, for a total of 14.

• Provide students with a copy of BLM 12.1-X Charged and Neutral Atoms for practice in classifying atoms by their charge.

• Have students complete Try This: Testing Charged Objects.


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TRY THIS: TESTING CHARGED OBJECTS

Skills: Hypothesizing, Observing, Communicating

Purpose • To observe interactions of objects that have been given an electric charge

Equipment and Materials (per group): acetate strips (2); ring clamp; retort stand; vinyl strips (2); thread; tape; paper towels

Notes • Sheets of acetate are available from science supply stores or your can cut strips from transparencies or sheet protectors.

Thin sheets of vinyl are available from craft stores. • Students should observe that the two acetate strips repel each other and the two vinyl strips repel each other, but the

acetate strip and the vinyl strip attract each other.

Suggested Answers A. Objects with similar charges repel each other.

B. Objects with different charges attract each other.

C. Sample answer: If an object with more electrons than protons is brought near an object with more protons than electrons, the objects will attract each other. If two objects that have more electrons than protons, or two objects that have more protons than electrons, are brought near each other, they will repel each other.

• Have students study Figure 4 on page 462 of the Student Book and relate it to their observations in the Try This: Testing Charged Objects.

• Point out that the Law of Electric Charges is similar to the magnetic attraction and repulsion between poles of a magnet in that like poles repel and unlike poles attract. Caution students, however, that although the magnetic force and electric force are related, they are not the same thing.

• Have students complete Try This: Moving Objects by Charging on page 463 of the Student Book.

TRY THIS: MOVING OBJECTS BY CHARGING

Skills: Predicting, Performing, Observing, Communicating

Purpose • To investigate the attractive and repulsive forces between charged objects

Equipment and Materials (per group): balloon; wool cloth; foam pellets (or puffed-rice cereal); packets of salt and pepper; blank white paper

Student Safety: Remind students that they should never eat or taste any materials they use in labs.

Notes • Rubbing the balloon with wool gives it a positive charge. Bringing the positively charged balloon near the foam pellets,

cereal, salt, or pepper induces a negative charge in them. • If students have difficulty answering question B, explain that both the salt and the pepper become charged. Suggest that

they consider how the gravitational force affects their results.

Suggested Answers A. As the distance decreased, the electric force from the balloon became stronger.

B. The balloon’s electric force is weak. Therefore, it can attract objects only if it is stronger than the downward gravitational pull on the objects. Doing this is possible only for lightweight materials.

C. You can charge the balloon and bring it close enough only to attract the lightweight pepper, but not close enough that the pull is enough to attract the heavier salt.


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Extend and Assess

• Ask a student volunteer to read the opening paragraph on page 460 aloud again. Ask questions that encourage students to apply what they have learned in this section. For example, ask, What caused the shock described in the paragraph? (An electric charge caused the shock.) What must be true about the electric charges when a person gets shocked by a metal doorknob? (The doorknob must have a charge opposite to that of the person’s hand.)

• Have students complete the Check Your Learning questions on page 463 of the Student Book.

CHECK YOUR LEARNING—SUGGESTED ANSWERS

1. Atoms are neutral because they have equal numbers of positively charged protons and negatively charged electrons.

2. (a) Electrons move most easily from one material to another.

(b) Neutral objects that gain electrons become negatively charged, and neutral objects that lose electrons become positively charged.

3. Sample answer: The diagram shows a model sodium atom. The protons and neutrons are bound in the nucleus. The electrons move in the space around the nucleus. Because the electrons are more loosely bound, if they have enough energy, they can move to other atoms. It is these loosely bound electrons that can transfer charge between objects.

<insert art, size C, grayscale, sodium model with 11 electrons, use style of Grade 9, Chap. 6, Fig. 5>

4. A neutral object has equal numbers of protons and electrons. A negatively charged object has more electrons than protons.

5. The object is now positively charged. It has more positive charges than negative charges because some of its electrons were transferred to the wool.

6. Object C must be positively charged. If object A is negatively charged and is attracted to object B, then object B must be positively charged. Because object C is repelled by object B, they must have the same charge, and object C must also be positively charged.

DIFFERENTIATED INSTRUCTION • Kinesthetic learners may benefit from making models of positively charged,

negatively charged, and neutral atoms. Give students three different colours of beads, buttons, or candies. Assign one colour to be protons, one to be neutrons, and one to be electrons. Have students make models of charged and neutral atoms by adding and removing particles. If they have difficulty identifying whether an atom is positive, negative, or neutral, suggest they pair up the “protons” and “electrons” to determine whether there are equal numbers.

LITERACY TIPS AND ENGLISH LANGUAGE LEARNERS • Students may be used to hearing the terms positive and negative used as value

judgements. Explain that the terms have no values associated with them when they refer to electric charge—that is, a positive charge is not “better” than a negative charge.


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Time 45–60 min Vocabulary • electric force • electric charge • neutral • neutral object • negatively charged object • positively charged object • Law of Electric Charges Skills Hypothesizing Predicting Performing Observing Communicating Lesson Materials per student • 2 acetate strips • ring clamp • retort stand • 2 vinyl strips • thread • tape • paper towels • balloon • wool cloth • foam pellets or puffed-rice cereal • packets of salt and pepper • blank white paper Assessment Resources Assessment Rubric 1: Knowledge and Understanding Assessment Rubric 2: Thinking and Understanding Assessment Summary 1: Knowledge and Understanding Assessment Summary 2: Thinking and Investigation Other Program Resources BLM 12.1-X Charged and Neutral Atoms Skills Handbook 3: Scientific Inquiry Skills Science Connections 9 website www.nelson.com/scienceconnections/9

Related Resources Schafer, Larry. Taking Charge: An Introduction to Electricity. NSTA Press, 2000. Science Connections 9 ExamView® Test Bank Science Connections 9 Teacher eSource SUITE Upgrade Science Connections 9 website www.nelson.com/scienceconnections/9


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12.2 Static Electricity and Discharges

OVERALL EXPECTATIONS: E2, E3


Developing Skills of Investigation and Communication: E2.1

Understanding Basic Concepts: E3.1, E3.2 The full Overall and Specific Expectations are listed on pages xx–xx.


object.

• There are many useful applications of static electricity.


• define static electricity

• relate an electric discharge to the movement of electrons between objects

• explain that lightning is a natural discharge of electrical energy

• identify uses of and problems caused by static electricity

SCIENCE BACKGROUND

Lightning • In Canada, the most frequent lightning

strikes occur in southwest Ontario. • Lightning kills between 6 and 10 people a

year in Canada and injures up to 70 a year. Faraday Cage • A device that shields its inside from static

electricity is called a Faraday cage. The cage must be made of a conducting material. When electric charge is applied to the cage, the charges repel each other and spread out over the outside of the device. The inside of the cage is safe because outside of the cage conducts the electricity to the ground. The spherical domes on van de Graaff generators, shown in figures throughout this chapter, are examples of Faraday cages.

Lightning Strikes on Airplanes and Cars • People travelling inside airplanes and cars

are protected from lightning strikes because of the skin effect. A Faraday cage applies to static charge uniformly spread over a conducting surface. A lightning strike is different. The voltage of lightning might increase and decrease drastically during a single strike. A changing electric field produces a magnetic field, and magnetic fields exert a force on electric charges. When lightning strikes an airplane or car, the magnetic field produced by it pushes the charge to the outside of the vehicle, forming a thin layer, or skin. The result is similar to a Faraday cage in that the electricity does not pass through the interior.


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POSSIBLE MISCONCEPTIONS – Identify: Many students think that lightning, shocks from metal objects, and

other discharges are static electricity. – Clarify: Static electricity is an imbalance of charge on an object. Lightning

and shocks are movements of electric charge that occur because of an imbalance of charge. Therefore, although lightning is caused by static electricity, lightning itself is current electricity.

– Ask What They Think Now: At the end of the lesson ask, What is wrong with the statement “Lightning is an example of static electricity”? (A lightning bolt is made of moving charges. Static electricity consists of charges that are not moving.)

TEACHING NOTES

Engage

• Bring in sheets of vinyl or vinyl letters from a craft store. Demonstrate how they can stick to surfaces. Allow students to experiment with the vinyl and infer why they stick to surfaces.

Explore and Explain

• Ask students if they have ever seen a demonstration with a van de Graaff generator, as in Figure 1 on page 464 of the Student Book. If any have, ask them to describe what they saw.

– Ask, Why does the girl’s hair stand out? (Each strand of hair has the same charge. The hair stands out because similar charges repel each other.)

– Ask, What do you think happens to the extra charge after the girl removes her hand from the van de Graaff generator? (The charge slowly dissipates into the air.) Explain that the girl will slowly lose the extra charge, but if excess charge suddenly leaves an object, it is called an electric discharge.

• Bring in an anti-static wrist strap (the type with a grounding wire) used by computer technicians. Explain that extra charge on a technician’s body moves along the wire and to the ground instead of onto sensitive electronics.

• Figure 2 on page 465 of the Student Book shows a simplified version of how lightning forms.

– Ask, Why do you think the positively charged particles move up and the negatively charged particles move down? (Positively charged particles are lighter because they have fewer electrons.)

– The ground becomes positively charged by induction, which students will learn about in Section 12.5. The negative charges at the base of the cloud repel electrons on the ground, inducing a positive charge.

– Point out the leader lines in the lightning strike. Explain that the charge buildup at the base of the cloud and on the ground leads to a series of events that cause an electric discharge. The path can be jagged because the forces between different parts of the cloud and ground are not uniform.


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• Draw students’ attention to the cloud-to-cloud lightning in Figure 3 on page 466 of the Student Book. Explain that there are many types of lightning other than cloud-to-ground. Challenge interested students to investigate and prepare a report for the class about the different forms, such as ball lightning, sheet lightning, and blue jet lightning.

• Ask students to study the printing process on page 467 of the Student Book. Ask, Why do the toner particles stick only to certain areas of the paper? (is the particles are attracted only to the parts of the paper that are given a negative charge by the laser.) Would the process work if the drum were negatively charged instead of positively charged? (yes, but only if the toner were negatively charged)

Extend and Assess

• Ask students to name a time when they experienced an effect from static electricity in their homes or in the community. Have them use what they have learned about static electric and charged particles to explain what happened.

• Students have read in this lesson about two practical uses of static electricity— static-cling film and photocopiers—but there are other important uses as well. Have students research one of these uses and report their findings to the class.

• Provide students with a copy of BLM 0.0-8 Term Box. Instruct them to write Static Electricity in the centre circle. Then ask them to fill out the parts of the graphic organizer to review what they have learned in this section.



1. When your socks rub against the rug, electrons move from the rug to you and you become negatively charged. When you touch the metal doorknob, there is an electric discharge from you to the doorknob.

2. An electric discharge can damage sensitive computer circuits.

3. Each strand of the person’s hair becomes positively charged. Because the strands have the same charge, they repel each other, which causes them to stand on end.

4. (a) Wind in the clouds causes ice and water particles to rub against each other and become charged. Negatively charged particles move to the bottom of the cloud. Positively charged particles move to the top of the cloud.

(b) The negative charge at the base of the cloud causes a positive charge to build up at the ground. When the charge difference is great enough, a series of events leads to an electric discharge.

5. The drum of the copier is given a positive charge. Laser light produces a negative charge on parts of the drum where printing should be. Negatively charged ink particles are attracted to these parts. The image is transferred to the paper as it rolls along the drum.

6. Students should produce an advertisement that creatively explains the advantages of static cling signs and decals. Key points that the advertisement might include are that the signs and decals are removable and reusable, they can be produced in any colour, size, or shape, and they are inexpensive. Check also that advertisements also include a brief explanation of static electricity and how the adhesive properties of the signs and decals work.


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DIFFERENTIATED INSTRUCTION • If possible, allow students to experiment with a small van de Graaff

generator. Kinesthetic learners will benefit from the hands-on experience. Ask verbal learners to describe in their own words what occurs in the generator. Have visual learners draw diagrams that illustrate the process.

LITERACY TIPS AND ENGLISH LANGUAGE LEARNERS • Students may confuse discharge with charge. Remind them of the meaning

of the prefix dis-. Explain that a discharge is a movement of charge; after a discharge, objects have no net charge.

Time 45–60 min Vocabulary • static electricity • electric discharge Assessment Resources Assessment Rubric 1: Knowledge and Understanding Assessment Summary 1: Knowledge and Understanding Other Program Resources BLM 0.0-8 Term Box Science Connections 9 website www.nelson.com/scienceconnections/9

Related Resources Rakov, Vladimir A. and Uman, Martin A. Lightning: Physics and Effects. Cambridge University Press, 2007. Friedman, John. Out of the Blue: A History of Lightning: Science, Superstition, and Amazing Stories of Survival. Delta, 2009. Science Connections 9 ExamView® Test Bank Science Connections 9 Teacher eSource SUITE Upgrade Science Connections 9 website www.nelson.com/scienceconnections/9

Reading Tip

Challenging Beliefs Ask students to identify statements in this section that contradict things they think they already know. Have them discuss how the information in the section contradicts their ideas and what they could do to better understand the contradictions and figure out whether their ideas are correct.

Biology Connection Some scientists think that the immense power of lightning strikes was the critical trigger that first bonded elements into compounds and initiated the evolution of organisms on Earth. Have students research this topic and prepare a short presentation for the class to describe what they learn.


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12.3 Charging by Contact

OVERALL EXPECTATIONS: A1, E3


Scientific Investigation Skills: A1.5, A1.11




object.



• explain how materials can become charged by friction

• compare the charges of two materials as a result of charging by friction

• compare the charges of two materials as a result of charging by contact

• describe conditions that cause two objects in contact to have balanced charge

SCIENCE BACKGROUND

Electrostatic Series • Materials can be classified according to

their tendency to become positively or negatively charged (or polarized). The following is a sample list of common materials, ranked from most likely to become positively charged to most likely to become negatively charged: glass, human hair, wool, silk, aluminum, paper, hard rubber (ebonite), copper, plastic wrap, vinyl.

• When two materials on the list rub together, electrons have a tendency to move from the material more likely to become positively charged to the material more likely to become negatively charged.

• The closer materials are together on the list, the less likely that contact will cause them to become charged.

Charging Conductors and Insulators • It might seem that charging a material

would be easiest for conductors, but in fact the opposite is true. When a charged object is brought near a conducting material, electrons easily transfer to the material. However, these electrons quickly spread over the conducting surface. The charge at the point of contact is minimal. When a charged object is brought near an insulating material, electrons respond by being either attracted or pushed away. A charge is either induced or transferred to the material. Unlike with a conducting material, however, this charge does not easily spread throughout the insulating material. The charge therefore remains strong at the point of contact.


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TEACHING NOTES

Engage

• Review concepts that students need to know in order to study this section. – Ask, What do we mean by contact forces and non-contact forces? (Contact

forces act only when objects touch. Non-contact forces can act both when objects touch and at a distance.) What are examples? (Sample answer: Pushing and pulling on a box is a contact force. Gravity, magnetism, and the electric force are non-contact forces.) Ask student volunteers to demonstrate the concepts by pushing a desk and dropping an object to the ground. Explain to students that in this section they will learn about how the electric force can charge objects that touch. In Section 12.5, they will learn how the electric force can charge objects that do not touch.

– Ask, What is friction? (Friction is a force between two touching objects that resists the movement of the objects past each other.) Have a volunteer demonstrate friction by pushing a desk. Tell students to rub their hands rapidly against each other to feel the thermal energy that results from friction. Explain that in this section they will learn how friction can transfer electric charge.

Explore and Explain

• After students read Charging by Friction, have them look at Figure 1 on page 468 of the Student Book.

– Ask, What is the charge of the comb and hair before the hair is combed? (Both are neutral.) What are their charges after combing? (The comb has a negative charge and the hair has a positive charge.)

– Ask, Would it be possible for both to end up with a positive charge? Explain. (No. Because of the law of conservation of charge, charge can be transferred but not be created.)

– Ask, Would it be possible for the charge to be the result of proton transfer? Explain. (No. Only electrons are held loosely enough to move to other atoms.)

• Invite students to recall a time when they have experienced electric shock. Ask them if they can remember whether it was on a dry day or a rainy day, and whether it was in the winter or in the summer.


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• Have students complete Try This: Charging by Contact. TRY THIS: CHARGING BY CONTACT

Skills: Performing, Observing, Communicating

Purpose • To investigate how neutral objects can be charged by simple contact, without rubbing

Equipment and Materials (per group): roll of clear adhesive tape

Notes • For Step 4, tell students to keep a small bit of the end of the tape off the desk so that they can easily lift up the piece of tape

to remove it from the desk. • Tell students to move the tape slowly by bringing it near the desk and near another piece of tape.

Suggested Answers A. The pieces of tape must have been charged when they were first pulled off the roll because they repelled each other.

B. The pieces of tape are neutral. They neither repel nor attract each other. Moisture in the breath removed the charge by attracting electrons.

C. Touching the neutral tape to the desk caused it to be charged. Some electrons travelled from the desk to the tape. D. If the pieces of tape touch, charge will equalize and the two pieces will no longer attract or repel each other.

• After students read page 470 of the Student Book, ask, How is the method of charging an object shown in Figure 3 different from the method shown Figure 1 on page 468? (In Figure 1, the comb moved. In Figure 3, the objects only touch.) Would charging by conduction work even if the sphere in Figure 3 were made of rubber instead of metal? Explain. (yes, although the charge would remain close to the point of contact between the metal rod and the rubber sphere)

• Have students read Conduction Between Two Charged Objects. Draw several large negative signs on three small index cards. One card should have more negative signs than the other two. Tell students that the cards are models for negatively charged objects. The card with more negative signs has a greater negative charge. Invite a student volunteer to use these models to demonstrate for the class the main points about conduction between two objects with the same charge:

(1) If the charges are the same but equal, the objects will repel.

(2) If the charges are the same but one has more charge, touching them causes charge to move to the object with less charge.

Extend and Assess

• Challenge interested students to plan and carry out an investigation in which they test the effect of humidity on the ability of one object to charge another object by friction.

• Distribute copies of BLM 0.0-7 Science Idea Box. Have students write Charging by Friction and Charging by Conduction inside the boxes, and then to add facts on both sides of the boxes to summarize what they have learned about the topics in this section.



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1. (a) A cat rubbing against a balloon results in charging by friction.

(b) The cat’s fur and the balloon have opposite charges. The cat’s fur becomes positively charged and the balloon becomes negatively charged when the two come in contact.

2. (a) If you bring a negatively charged metal pie plate in contact with a neutral glass rod, electrons will move to the neutral glass rod.

(b) The glass rod will be negatively charged.

3. Water molecules in the air will drain the charge from the decal. The neutral decal will not stick to other surfaces.

4. When the rods touch, electrons will move from the less positively charged to the more positively charged rod. Eventually the rods will have the same amount of positive charge.

5. (a) When the rod touches the sphere, electrons will move from the sphere to the rod.

(b) The sphere will acquire a positive charge.

DIFFERENTIATED INSTRUCTION • Kinesthetic and visual learners will benefit by modelling the process of

charging by contact. Give students small objects to represent electrons and have them place the objects on drawings of two objects. Then ask the students to move the electrons between the objects to show how contact can charge an object.

LITERACY TIPS AND ENGLISH LANGUAGE LEARNERS • Review the meaning of the term conduct with students. Ask them to explain

how the meaning of conduct can help them remember what conduction is. Time 45–60 min Vocabulary • charging by friction • charging by conduction Skills Performing Observing Communicating Lesson Materials per student • roll of clear adhesive tape Assessment Resources Assessment Rubric 1: Knowledge and Understanding Assessment Rubric 2: Thinking and Investigation Assessment Summary 1: Knowledge and Understanding Assessment Summary 2: Thinking and Investigation Other Program Resources BLM 0.0-7 Science Idea Box Skills Handbook 3: Scientific Inquiry Skills Science Connections 9 website www.nelson.com/scienceconnections/9


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Related Resources Short, Harold, et al. “How Do Geckos Stick? The Science Teacher, NSTA Press,

November 1, 2008. Science Connections 9 ExamView® Test Bank Science Connections 9 Teacher eSource SUITE Upgrade Science Connections 9 website

www.nelson.com/scienceconnections/9

Reading Tip

Evaluating Lead students in brainstorming examples of charging by contact that they have experienced in their everyday lives. Record students’ ideas and ask them to describe how the explanations in this section can explain their observations.

At Home If students have carpeting or a rug in their homes, suggest they try shuffling across it in stocking feet and then touching a metal door handle. Do they feel a shock? Ask them to try doing this on a dry day and then on a humid or rainy day. Have them describe their results to the class.


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12.4 Conduct an Investigation: Charging Objects by Contact



Scientific Investigation Skills: A1.1, A1.5, A1.8, A1.10, A1.11




object.



• transfer charge from a positively or a negatively charged object to a neutral object by contact

• apply the Law of Electric Charges to infer the type of charge the neutral object gets during charge by contact with either a positively or a negatively charged object

SCIENCE BACKGROUND

• Pith is a lightweight, spongy material found in the centre of vascular plant stems. It is useful in electrostatic investigations because its low mass means the gravitational force on it is low enough to allow the pith to respond easily to electric forces on it. With a pith ball electroscope, the effects of electrostatic charges can easily be observed.

• When a negatively charged object, such as a charged ebonite rod, approaches the pith ball, electrons in the area of the pith ball nearest the rod experience a repulsive electric force and move away. This leaves a positively charged area nearest but not touching the negatively charged rod.

• The pith ball is not a conductor. As a result, the positive charge does not spread out over its surface.

• When the negatively charged ebonite rod actually touches the pith ball, electrons move from the rod into the pith ball. The pith ball then becomes negatively charged as well.

• The reaction to the pith ball from a Lucite rod is similar, except the charges are opposite. When the positively charged Lucite rod is very near but not touching the pith ball, the positive charge of the rod attracts electrons in the pith ball, giving it a negative charge near the region. When the rod actually touches, however, electrons move from the pith ball into the rod.


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TEACHING NOTES

Student Safety

• Ask students if they are allergic to any of the materials used in the activity. If someone is, use the electrostatic series to identify replacements.

• Have students work in small groups to perform the activity.

Testable Question • Explain to students that the testable question does not have to be answered

explicitly, but that they should think about the Law of Electric Charges when they make their hypotheses.

Hypothesis/Prediction • Sample hypothesis: If I touch a neutral object with a charged object, the

neutral object will then have the same charge as the charged object because electrons will move between the objects.

Experimental Design • Tell students that they will make a general hypothesis before the activity and

also make a prediction in Step 8 of the investigation.

Equipment and Materials • Have students use BLM 12.4-X Conduct an Investigation: Charging Objects

by Contact to record their data for this investigation.

Procedure • Emphasize to students that, to obtain reliable results, they must discharge the

pith ball and rods by touching them with their fingertips after each series of tests.

Analyze and Evaluate (a) Sample answer: Yes, the observations support my hypothesis. I observed

that the neutral object acquired the same charge as a charged object that touched it.

(b) When touched by a negatively charged ebonite rod, the neutral pith ball also became negatively charged and was repelled by the ebonite rod. When touched by a positively charged Lucite rod, the neutral pith ball also became positively charged and was repelled by the Lucite rod.

(c) Sample answer: According to the Law of Electric Charges, objects with similar charges repel and objects with opposite charges attract. I knew the ebonite rod gave the pith ball a negative charge because the rod repelled the ball. I knew the Lucite rod gave the pith ball a positive charge because the rod repelled the ball.


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DIFFERENTIATED INSTRUCTION • Allow students to choose how they document their results. For example,

visual learners may choose to draw diagrams, and verbal learners may prefer to write a description.

LITERACY TIPS AND ENGLISH LANGUAGE LEARNERS • The materials in this activity (e.g., pith, Lucite, ebonite) may be unfamiliar to

many students. Review with students the names of the various materials and ensure that they know which materials to use for each step. You may wish to provide labelled materials for students to refer to.

Time 45–60 min Skills Hypothesizing Predicting Performing Observing Analyzing Evaluating Equipment and Materials per student • pith ball electroscope • ebonite rod • Lucite rod • wool cloth • nylon cloth Assessment Resources Assessment Rubric 5: Conduct an Investigation Assessment Summary 5: Conduct an Investigation Self-Assessment Checklist 1: Conduct an Investigation Other Program Resources BLM 12.4-x Conduct an Investigation: Charging Objects by Contact Skills Handbook 3: Scientific Inquiry Skills Science Connections 9 website www.nelson.com/scienceconnections/9

Related Resources Ford, Richard. Homemade Lightning: Creative Experiments in Electricity. McGraw-

Hill/TAB Electronics, 2001. Science Connections 9 ExamView® Test Bank Science Connections 9 Teacher eSource SUITE Upgrade Science Connections 9 website



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12.5 Charging by Induction



Scientific Investigation Skills: A1.5, A1.10, A1.11

Developing Skills of Investigation an Communication: E2.1, E2.3



object.



• explain how objects can be charged by induction

• identify whether charge by induction is temporary or permanent

• describe how charge by induction explains why neutral objects are always attracted to charged objects

• compare the charges of objects after charge by induction has occurred

SCIENCE BACKGROUND

Grounding of Buildings • To protect a building or other structure

from experiencing electric discharge, a lightning rod is erected atop the building to provide grounding in the event of a lightning strike. A basic system typically involves a vertical metal rod placed so that it is taller than the highest point of a structure. A conducting cable attached to the rod extends to the ground. A ground rod is sometimes used to direct the cable into the ground. If lightning strikes the lightning rod, the electric charge moves safely to the ground. Several lightning rods might be installed on wide structures. Towers also have complex systems that might include many lightning rods and conductors.

Electric Field • Every electric charge has a surrounding

area in which other charges experience a push or pull. This area, called the electric field, does not have a clear point at which it ends. It just becomes continually weaker with distance away from the charge.

• Electric fields are responsible for charge by induction. Every charged object is surrounded by an electric field, which is a combination of the fields of each of the object’s electric charges. When the charged object is brought close to a neutral object, the field of the charged object pushes on the neutral object’s charged particles. The effect of the field is stronger as the two objects get nearer.


23

TEACHING NOTES

Engage

• Use this simple demonstration to initiate a discussion of induction. – Before class, inflate several balloons and, with a hole-punch, make a pile

of small paper circles. – Ask for several student volunteers to come to the front of the class. Give

each volunteer an inflated balloon and some paper circles. They can set the paper circles in front of them on the floor or on a table. To ensure the balloons are well grounded, wipe them with a slightly damp paper towel before giving them to the students.

– As the rest of the class watches, have the volunteers bring their balloons near but not touching the paper circles. Because the balloons are neutral, they will not pick up the paper. Next, ask the volunteers to rub their balloons against wool (e.g., against a sweater or blanket you bring in to class) and again to bring the balloons near but not touching the paper circles. Ask the class to use what they have learned about electric charge to infer why the balloons now attract the paper.

Explore and Explain

• After students read Induced Charge Separation on page 474 of the Student Book, provide a student volunteer with a balloon and a piece of wool to charge it. Have the student use the balloon to demonstrate and explain the charge by induction described in Figure 1. Make sure students understand two main points about charging by induction: (1) The objects do not touch. (2) The induced charge is opposite that of the original charged object.

• Draw students’ attention to the following sentences on pages 474 and 475 of the Student Book:

When you rub a balloon against your sweater, the balloon gains a negative charge due to contact.

When you rub a balloon with a polyester cloth, the balloon loses electrons and gains a positive charge by contact.

Students may think that objects have the ability to be either positively charged or negatively charged. Use these sentences to help students understand that when objects touch, the direction of electron transfer depends on which of the objects has the greatest tendency to gain electrons.

• After students read about grounding and discharge, ask, What is the purpose of grounding? (to safely remove excess charge from a person or object) In which direction do electrons move during grounding? (When grounding a negatively charged object, electrons move from the object toward the ground. When grounding a positively charged object, electrons move from the ground toward the object.)

• Have students complete Try This: Storing Static Electricity.


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TRY THIS: STORING STATIC ELECTRICITY

Skills: Observing, Communicating

Purpose • To apply charging by induction to build a device that stores static charge

Equipment and Materials (per student): clear plastic tumbler or Styrofoam cup; glue or tape; aluminum pie plate; Styrofoam dinner plate; piece of wool cloth; paper clip; modelling clay

Notes • The Styrofoam plates will have a positive charge when they are removed from packaging. Wipe them with a damp cloth to

remove the charge. In Step 1, make sure students rub the plates a full minute to give them a negative charge. • The aluminum pie plate becomes charged when it is placed on the negatively charged foam plate. Touching the pie pan

makes the charge permanent, similar to the effect shown in Figure 5 on page 477 of the Student Book. This permanent charge is stored on the pie plate. It is discharged when the pie plate is brought close to the metal paper clip.

Suggested Answers A. Sample answer: I received a small shock.

B. Sample answer: I saw a spark.

C. Sample answer: I saw a spark when I brought the edge of the pie plate near metal objects. D. Touching the pie plate could cause a shock. It would also discharge the pie plate.

Extend and Assess

• Provide students with a copy of BLM 0.0-2 Venn Diagram. Have them use the diagram to compare and contrast charge by contact and charge by induction.

• Have students complete the Check Your Learning questions on page 479 of the Student Book. CHECK YOUR LEARNING—SUGGESTED ANSWERS

1. (a) Static cling on clothes is charge by friction, not by induction, because the clothes rub against each other.

(b) Bringing a charged rod near a neutral electroscope is charge by induction because the charged rod causes charge separation in the electroscope without touching it.

(c) Attracting pieces of foam with a charged comb is charge by induction because the comb causes charge separation in the foam pieces without touching them.

(d) Hair standing on end after you have taken off a hat is charge by contact, not by induction, because the hat and hair have been touching.

2. (a) The charge on the side of the aluminum lid is positive. Some of the negative charge has moved to the upper part of the lid, leaving more positive charge near the bottom.

(b) If I touch the aluminum lid with my finger, electrons will move from the lid into my finger. The positive charge that was induced in the lid by the Styrofoam block will then be permanent. The lid will have a positive charge.

(c) The lid will have a permanent positive charge.

(d) The Styrofoam block was charged by contact.

(e) The lid was permanently charged by induction.

3. Sample answer: The balloon is negatively charged and the hair on my arm is neutral at the start of the experiment. As the balloon gets closer, the electrons in my arm hair are repelled, and the hair becomes positively charged. This positive charge causes the hair to be attracted to the balloon, and it will also cause the separate hairs to repel each other.


4. A sample diagram is shown below.

5.

6.

DIF• Us

coThfor

LIT• Stu

angro

Tim45–6Voca• ind• ch• groSkillObseComLessper s• cle• glu• alu• Sty• pie• pa• mo

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The rod must have been positively charged. Because the pith ball repels a negatively charged strip of plastic, it must now be negatively charged. The rod must have been positively charged in order to induce a negative charge in the pith ball.

(a) The positively charged rod is attracting the pith ball’s electrons. Because the rod and the right side of the pith ball have opposite charges, they are attracted to each other.

(b) If I touch the ball while the rod is near, electrons will be drawn from the ground through me and into the ball. This will give the pith ball a permanent negative charge.

FERENTIATED INSTRUCTION e Figures 1–5 in this section to engage students in a class review of the ncepts. Have different students describe the steps shown in each figure. en ask other students to summarize the concepts using methods appropriate different learning styles.

ERACY TIPS AND ENGLISH LANGUAGE LEARNERS dents may have difficulty understanding that ground can be both a noun

d a verb. Give them several sentences and ask them to identify whether und is a noun or a verb in each sentence.

e 0 min bulary uced charge separation

arging by induction unding s rving municating on Materials tudent ar plastic tumbler or Styrofoam cup e or tape minum pie plate rofoam dinner plate ce of wool cloth

per clip delling clay


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Assessment Resources Assessment Rubric 1: Knowledge and Understanding Assessment Rubric 2: Thinking and Investigation Assessment Summary 1: Knowledge and Understanding Assessment Summary 2: Thinking and Investigation Other Program Resources BLM 0.0-2 Venn Diagram Skills Handbook 3: Scientific Inquiry Skills Science Connections 9 website www.nelson.com/scienceconnections/9

Related Resources Understanding: Electricity, Discovery School. Science Connections 9 ExamView® Test Bank Science Connections 9 Teacher eSource SUITE Upgrade Science Connections 9 website


Reading Tip

Checking for Bias Review with students examples of clue words that can indicate bias, such as better than, worse than, best, and worst. Tell students that they can use a two-column table to record the advantages and disadvantages presented in a text. Using the table will make it easier for them to determine whether the information presented is biased.


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12.6 Perform an Activity: Charging Objects by Induction







object.



• induce an electric charge on paper circles

• induce an electric charge on water

• use a metal leaf electroscope to test whether an object is charged or uncharged

SCIENCE BACKGROUND

• A metal leaf electroscope is a static electricity indicator. A metal knob is attached to the two metal leaves. When a charged object is brought near the knob, the knob becomes charged. If the knob is negatively charged, it draws electrons away from the metal leaves. If the knob is positively charged, it pushes electrons toward the leaves. Either way, the leaves have the opposite charge to the knob. However, because they have the same charge, they repel each other and spread apart. The greater the charge on the knob, the farther apart the leaves will be.

• Touching the knob will ground it. The knob and the leaves will become neutral and the leaves will slowly move closer.

• The electroscope can be charged by induction or by contact. The table shows the possible ways:

Rod charge and action

Resulting charge on the knob

Action by the leaves

negative; near the knob

positive spread apart

negative; touch the knob

negative spread apart

positive; near the knob

negative spread apart

positive; touch the knob

positive spread apart


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TEACHING NOTES

Student Safety

• Ask students if they are allergic to any of the materials used in the activity. Provide replacements if necessary.

• Tell students that they will use a metal leaf electroscope for this activity. Explain that the leaves of an electroscope are lowered and together if they are neutral. The leaves repel and rise if they are charged.

• Have students work in small groups for this activity.

Purpose • Students will use the electroscope to test whether objects have been charged.

Equipment and Materials • Ensure that the electroscopes are working properly and are uncharged.

• Alternative materials are: fur for wool cloth; Lucite or glass for the plastic rod; and silk for the polyester cloth.

Procedure • Provide students with a copy of BLM 12.6-X Perform an Activity: Charging

Objects by Induction to record their data.

• Caution students to read each step carefully before performing it. Each step depends on whether the rods and electroscope are neutral or charged.

Analyze and Evaluate (a) The uncharged rods did not affect any of the materials. When charged, both

rods attracted the paper circles and the stream of water. They both made the leaves of the electroscope move apart.

(b) The electroscope was charged by induction in Steps 5 and 7.

(c) When a charged object is placed near an uncharged one, the uncharged object becomes attracted to the charged object.

(d) The attraction becomes stronger as the distance between the charged and uncharged objects decreases.

(e) Sample answer: You could bring an uncharged object near the object you want to test. If the object is neither attracted nor repelled, it is uncharged.

(f) No. You could not tell if a charged electroscope was positively or negatively charged by looking at it. The leaves separate in both cases.

(g) First bring the rod with a known charge near a charged electroscope and record the result. Next bring the rod with an unknown charge near the electroscope. If the result is the same, the rods have the same charge.


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DIFFERENTIATED INSTRUCTION • Verbal and auditory learners will benefit from reading the instructions aloud

or listening to them being read. Pair all students in the class and have one student in each pair read each line in the instructions to the other student. Instruct students to stop and discuss any steps they do not understand.

LITERACY TIPS AND ENGLISH LANGUAGE LEARNERS • Provide sentence frames for English language learners to use to answer the

questions and record their observations. An example of a sentence frame is When a charged object is placed near an uncharged object,_____________.,

Time 45–60 min Skills Questioning Controlling Variables Performing Observing Analyzing Evaluating Equipment and Materials per student • metal leaf electroscope • ebonite rod • wool cloth • polyester cloth • clear plastic rod • paper circles (from a hole-punch) Assessment Resources Assessment Rubric 6: Perform an Activity Assessment Summary 6: Perform an Activity Self-Assessment Checklist 2: Perform an Activity Other Program Resources BLM 12.6-X Perform an Activity: Charging Objects by Induction Skills Handbook 3: Scientific Inquiry Skills Science Connections 9 website www.nelson.com/scienceconnections/9

Related Resources Assis, André Koch Torres. The Experimental and Historical Foundations of Electricity.

Apeiron, 2010. Science Connections 9 ExamView® Test Bank Science Connections 9 Teacher eSource SUITE Upgrade Science Connections 9 website



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12.7 Perform an Activity: Testing Materials for Electron Flow




Developing Skills of Investigation and Communication: E2.2, E2.3


KEY CONCEPTS • Electricity describes how electrons move from one place to another.

• Some materials allow electrons to move through them easily (conductors), while others do not let electrons move through them easily (insulators).


• explain how to use an electroscope to test whether a material resists or allows electron flow

• classify materials as allowing electron flow or resisting electron flows

SCIENCE BACKGROUND

• When you flip a light switch, the light immediately turns on. Current moves through a conducting wire at almost the speed of light (3 × 108 m/s). Particles in the wire cannot move that fast. This speed describes how fast charge is passed from particle to particle along the wire.

• In a conducting wire, electrons are the charge carriers. Consider, for example, a copper wire. At room temperature, the instantaneous speed of an electron in copper is about 1.6 × 108 cm/s. However, this speed is in random directions, not straight along the length of the wire.

• Electrons in a current-carrying wire have a net movement along the wire. The average speed of an electron moving from one point to another along the length of a conducting wire is called the drift velocity. The speed depends on various factors, such as the material from which the wire is made, the diameter of the wire, and the current. Electrons are also slowed by scattering. For example, a drift velocity might be about 0.37 mm/s. An electron might take about an hour to move 1 m in household wiring. An electron moving in a small DC circuit might move only 0.5 m in an entire day.


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TEACHING NOTES Student Safety

• Ask students if they are allergic to any of the materials used in the activity. Provide replacements if necessary.

• Instruct students to read the introductory paragraphs carefully to learn what they should observe in this activity.

• Have students work in small groups for this activity.

Purpose • Students will learn how a charged electroscope reacts when materials that

allow or resist electron flow are brought near it.

Equipment and Materials • Collect a variety of objects for each group to test. Include both conductors

and insulators. Test the reaction of the charged electroscope to the materials before students perform the activity. Sample conductors include a copper penny, graphite pencil lead, a brass fastener, and aluminum foil. Sample insulators include a plastic pen, a rubber eraser, a wood block, and a ceramic mug.

Procedure • Provide students with a copy of BLM 12.7-X Perform an Activity: Testing

Materials for Electron Flow to record their observations.

• Caution students that in order for their results to be valid, the electroscope must be charged before they bring each material close to it.

Analyze and Evaluate (a) Sample answer: The copper penny, pencil lead, brass fastener, and

aluminum foil allowed electrons to flow. The plastic pen, rubber eraser, wood block, and ceramic mug did not allow electrons to flow.

(b) Sample answer: You can classify the objects that allowed electron flow as conductors. You can classify the objects that do not allow electron flow as insulators.

Apply and Extend (c) Sample answer: I predicted that a metal ruler would allow electrons to flow,

but a plastic ruler would not. My observations supported my predictions: the metal ruler allowed electrons to flow, and the plastic ruler did not allow electrons to flow.

DIFFERENTIATED INSTRUCTION • Help students understand the procedure by suggesting different approaches to

the material. For example, they may wish to draw sketches of what they should do at each step, or read the steps and explain them to a partner.


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LITERACY TIPS AND ENGLISH LANGUAGE LEARNERS • Review the meaning of the roots electr- and scope with students. Ask them to

explain how the meanings of those roots relate to the definition of electroscope.

Time 45–60 min Skills Predicting Controlling Variables Performing Observing Analyzing Evaluating Equipment and Materials per student • metal leaf electroscope • ebonite rod • wool cloth or piece of fur • testing materials Assessment Resources Assessment Rubric 6: Perform an Activity Assessment Summary 6: Perform an Activity Self-Assessment Checklist 2: Perform an Activity Other Program Resources BLM 12.7-X Perform an Activity: Testing Materials for Electron Flow Skills Handbook 3: Scientific Inquiry Skills Science Connections 9 website www.nelson.com/scienceconnections/9

Related Resources Gibilisco, Stan. Electricity Demystified. McGraw-Hill Professional, 2005. Science Connections 9 ExamView® Test Bank Science Connections 9 Teacher eSource SUITE Upgrade Science Connections 9 website


Unit Task Bookmark Remind students that what they have learned in this section about materials that resist or allow electron flow will be useful when they complete the Unit Task.


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12.8 Moving Charges



Career Exploration: A2.1



KEY CONCEPTS • Electricity describes how electrons move from one place to another.

• Current electricity is generated by moving electrons in a closed path.


• explain the difference between electrical conductors and electrical insulators

• compare and contrast direct current and alternating current

• describe how electric current travels through the electrical energy distribution grid

SCIENCE BACKGROUND

• Electrons exist at different energy levels in an atom. Those in the outermost energy level are valence electrons. The electrons an atom can most easily gain or lose are valence electrons because they are less tightly bound than other electrons. In metals, the valence electrons of all atoms are so loosely bound that they can move freely from atom to atom. This explains why metals are good electrical (and thermal) conductors: These free electrons can transport charge quickly and easily along an electrical wire.

• For a material to conduct electricity, its valence electrons must have enough

energy to move from one atom to another. For conducting materials, gaining enough energy is easy because the difference between the energy of the valence electrons and the energy needed, called the band gap, is low. For insulating materials, the valence electrons are held so tightly that the band gap is high. Gaining enough energy to break free and conduct charge along the material is difficult, but not impossible.

• The voltage of a circuit determines the energy that valence electrons have available to overcome the band gap and become free electrons.

TEACHING NOTES

Engage

• Have students pre-read the definitions of conductor on page 484 and insulator on page 485. Relate these definitions to the materials that students tested for electron flow in Section 12.7. Explain that in this section they will learn why the materials allow or prevent electron flow.


34

• Ask student volunteers to point to various devices that carry electricity in the classroom, such as electrical cords, computers, lamps, and clocks. Lead the class in analyzing materials used in the devices to decide which devices were likely chosen because they do not easily allow electron flow through them.

Explore and Explain

• Draw a model atom with energy levels on the board, similar to the model fluorine atom shown in Figure 1 on page 210 of the Student Book. Explain that the electrons in the outermost level are most loosely held to the atom. In fact, in metals, these electrons are held so loosely that they can flow freely among atoms. This is what makes metals, such as the copper wire in Figure 1 on page 484 of the Student Book, good conductors.

• Draw students’ attention to the correspondence between the conductivity series in Figure 4 and the list of conductors and insulators in Table 1 (both on page 485 of the Student Book).

• After students look at Figure 4 and Table 1, ask, Why do you think adding salt changes water from an insulator to a conductor? (Salt breaks apart in water into positively and negatively charged atoms, called ions. Unlike a solid conductor, in which electrons carry charge, in salt water these ions can carry charge.) Explain that in tap water and lake water, the ions are different, but the effect is the same. Most water is an electrical conductor.

• Read aloud the definition of electric current on page 486 of the Student Book. Ask, How is current electricity different from static electricity? (Current electricity is a continual flow. Static electricity is either stored or a sudden discharge.) What does a “closed path” mean? (It means that the current must loop around and eventually return to its origin.) and, Does the current that supplies energy to homes flow in a closed path? (Yes. It flows in a loop that extends from the generating plant to homes.)

• Have students study the diagram of the battery in Figure 5 on page 486 of the Student Book. Point out that the electrolyte paste and the zinc are necessary for the chemical reactions that cause an excess of electrons at the anode and a shortage of electrons at the cathode. Ask, In which direction do electrons move in the diagram? (Electrons move from the anode to the cathode.) Explain to students that this does not happen inside the battery. Batteries include a separator between the electrolyte and the zinc. Electrons move through a wire connected outside the battery to each terminal.


35

• Draw students’ attention to the transformers in Figure 6 on page 487 and read aloud the discussion of transformers in the last paragraph on the same page. Explain that the use of transformers is the primary reason that alternating current, rather than direct current, is employed in the distribution grid. Transformers change the push, or voltage, of current. With transformers, the voltage can be made high for long distances. Higher voltage transmission results in lower thermal loss of energy along the lines. Near homes, transformers are also used to decrease the voltage to low levels for safety. If direct current were used, only low voltage with high thermal energy loss could be used.

• Have students complete Citizen Action: Replacing Old Wiring. CITIZEN ACTION: REPLACING OLD WIRING

Purpose • To learn how to recognize signs of old wiring, and to inform others about how to protect their homes from the danger

Notes • Provide students with a copy of BLM 12.8-X Citizen Action: Replacing Old Wiring to help guide them in this activity. • Have students work in small groups. Ask students first to read the instructions and think about how they might complete the

activity. Then have groups brainstorm what they might do, the person or company they might contact, and the types of questions they might ask.

• Students will probably learn that frayed wires, insulation that has hardened and broken down, and faulty switches are common dangers from old home electrical systems. Electricians and electrical companies will probably suggest that homeowners hire a certified electrician to inspect and update the systems.

Extend and Assess

• Provide students with a copy of BLM 0.0-7 Science Idea Box. Tell them to write Conductor in one box and Insulator in the other. Then have them write facts about each on the sides to review what they have learned in this section.

• Have students complete the Check Your Learning questions on page 488 of the Student Book. CHECK YOUR LEARNING—SUGGESTED ANSWERS

1. (a) An iron nail is a conductor because iron is a metal. It has loosely held electrons and allows current to easily flow through it.

(b) A glass jar is an insulator because glass has tightly held electrons and does not allow current to easily flow through it.

(c) Dry air is an insulator because electrons cannot easily flow between the particles that make up air.

(d) A gold ring is a conductor because gold is a metal. It has loosely held electrons and allows current to easily flow through it.

(e) A carbon rod is a conductor because even though carbon is a nonmetal, its outermost electrons are not tightly bound and can fairly easily flow through it.

(f) A wooden spoon is an insulator because the electrons in wood are tightly bound and do not easily travel among atoms.

2. Pure water is non-conductive, but tap water and water in a pond, lake, or ocean is not pure. It contains dissolved minerals that can carry charge, making it a good conductor of electricity.

3. Dry cell batteries convert chemical energy into electrical energy.

4. To flow, electricity must be able to flow back to its source or else the current cannot continue. Water can flow without having to return to its source.


36

5. Sample answer: Static electricity and current electricity are alike because they both involve the motion of electrons. They are different because, with static electricity, the electrons tend to stay in one place until the difference in charge is great enough that it is rapidly transferred in an electric discharge. Electric current, however, is a constant flow that can only move if it has a closed path along which to travel.

6. Sample answer: I prefer a battery as a source of energy for my MP3 player because a battery is portable. I prefer plugging my computer into a wall socket because electrical energy is less expensive this way and because it does not run out of power like a battery does.

DIFFERENTIATED INSTRUCTION • Allow students to demonstrate their understanding of the difference between

conductors and insulators using a method of their choosing. For example, interpersonal learners may choose to do a demonstration or presentation, and kinesthetic learners may make models of electron flow.

LITERACY TIPS AND ENGLISH LANGUAGE LEARNERS • Many of the terms used in this section, such as conduct, insulate, and current,

have multiple meanings (and, in the case of conduct, multiple pronunciations). Review the various meanings of the terms with students, pointing out those meanings used in the section.

Time 45–60 min Vocabulary • conductor • insulator • conductivity • electric current • direct current (DC) • alternating current (AC) Assessment Resources Assessment Rubric 1: Knowledge and Understanding Assessment Summary 1: Knowledge and Understanding Other Program Resources BLM 12.8-X Citizen Action: Replacing Old Wiring BLM 0.0-7 Science Idea Box Science Connections 9 website www.nelson.com/scienceconnections/9

Related Resources Grigsby, Leonard (ed.). Electric Power Generation,Transmission, and Distribution. CRC

Press, 2007. Science Connections 9 ExamView® Test Bank Science Connections 9 Teacher eSource SUITE Upgrade

Science Connections 9 website www.nelson.com/scienceconnections/9

Reading Tip

Evaluating Diagrams Ask students to give examples of things they already know that relate to the figures in the Student Book. Have them discuss the examples and explain how they relate to the diagrams.


37

History Connection Thomas Edison insisted that direct current should be used for public electric energy distribution. Nikola Tesla, who had previously worked for Edison, developed a system based on alternating current. Have students research the controversy between the two inventors and prepare a presentation about the events that led to the system in use today.

Unit Task Bookmark Remind students that what they have learned about current electricity and the electrical energy distribution grid in this section will be useful when they complete the Unit Task.


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Tech Connect: Superconductors

TEACHING NOTES

Before Reading • Before students read the passage, review the meaning of the terms conductor

and insulator with them. Remind them that both terms can apply to temperature or to electricity. Although this passage does include references to temperature, the term conductor in the passage refers to a substance that allows electricity to flow through it.

• Distribute copies of BLM 0.0-1 K-W-L Chart and have students complete the Know and Wonder columns to record their current understanding of superconductors.

During Reading • After students read the first two paragraphs, say, The passage does not define

superconductor directly. But we can use context clues to infer the definition. Point out the signal words (examples include if and become) that indicate the connection between no electrical energy is lost as it passes through them and superconductors. Have students work as a class to come up with a definition of superconductor. Write the definition on the board.

• Remind students that electric current in a wire produces a magnetic field around the wire.

• Have students complete a Think/Pair/Share activity. Based on the information in the passage, have students infer ways that superconductors could be used for more efficient energy production and storage.

After Reading • Have students complete their K-W-L charts by filling in what they learned

about superconductors from the passage. They should also correct any errors in the Know column. Ask students to brainstorm ways they could address any unanswered questions from the Wonder column.

• Conclude by having students complete BLM 12.TC Tech Connect: Superconductors as OSSLT practice.

DIFFERENTIATED INSTRUCTION • Verbal/auditory learners may better understand the passage if they read it

aloud or listen to other students read it aloud. Interpersonal learners may prefer to discuss the content with a partner. To address both of these learning styles, have all students in the class read the passage in pairs, reading each paragraph aloud and then discussing it.


39

LITERACY TIPS AND ENGLISH LANGUAGE LEARNERS • Review the meaning of the prefix super- with students. Remind them that

although the word super can mean wonderful, fantastic, or great, the prefix super- nearly always means above, more, or greatest.

Time 30 min Literacy Resources BLM 12.TC Tech Connect: Superconductors BLM 0.0-1 K-W-L Chart Assessment Resources Assessment Rubric 1: Knowledge and Understanding Assessment Summary 1: Knowledge and Understanding Other Program Resources Science Connections 9 website www.nelson.com/scienceconnections/9

Related Resources Science Connections 9 ExamView® Test Bank Science Connections 9 Teacher eSource SUITE Upgrade Science Connections 9 website



40

Chapter 12 Looking Back

Key Concepts Summary • Referring to the concept map, remind students that the chapter Key Concepts

were introduced at the beginning of the chapter. Have students use the bulleted information to review the concepts.

• Ask one or two questions that will prompt students’ recall of each Key Concept. Have students explain and support their responses. Sample questions and responses are given below:

1. Why are electrons the charge carriers from atom to atom? (Electrons are the particles that are mostly loosely held in atoms.)

2. What does an imbalance of charge on an object’s surface mean? (One side has more negative charge and the other side has more positive charge.)

3. What is a way that static electricity is useful? (Sample answer: Static electricity causes ink to stick to paper in a photocopier.)

4. How can an object be charged without touching it? (A charged object induces a charge by attracting or repelling electrons in an uncharged object.)

5. How is current electricity different from static electricity? (Current electricity travels in a continuous loop, but static electricity is either stored or discharges quickly.)

6. Why is copper a better conductor than wood? (Copper is a metal, and its outer electrons are loosely held and able to carry charge. Wood holds it electrons tightly, and they cannot easily carry charge.)

• Organize the class into six groups and assign each group one of the Key Concepts in the concept map on page 490 of the Student Book. Ask each group to summarize the information in the chapter that relates to the Key Concept in their own words. Tell them that they should include in their summary an explanation of how the photograph shown in the concept map relates to their Key Concept. Have students share their summaries with the class.

What Do You Think Now? • Have students look at each of the pictures on page 491 of the Student Book.

Ask volunteers to describe how each picture shows something they have experienced in the past or something in everyday life, and to relate the photograph to the concepts in the chapter.


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• Use the following questions to help students form an opinion about each What Do You Think Now? statement.

1. Does static electricity flow in home electrical wiring? (No. Homes use current electricity.)

2. How do photocopiers and electricity each involve static electricity? (The ink sticks to the drum of the copier because of static charge attraction, and lightning is caused by static charge attraction between clouds and the ground or other clouds.)

3. What is happening to the girl in the picture, and does it harm her? (She is building up static charge from touching the generator, which causes all of the strands of hair to repel one another. This is not harmful, it is simply buildup of charge.)

4. Why is the water bending toward the comb? (The charged comb induces an opposite charge in the water and attracts it.)

5. What causes electric charge to move through wires? (The charge must have some push, or voltage, provided by the generating plant.)

6. In what ways do we take advantage of the properties of static electricity? (Sample answer: Some things that we use like cling wrap stick to other objects because of static charge attractions.)

• Remind students of the poll you took of the What Do You Think? questions before they studied the chapter. Poll the class again and compare the results of it with the results of the previous poll.

• Write the Big Idea on the board and draw a T-chart underneath. Label the two halves of the T-chart Static Electricity and Current Electricity. Lead students in brainstorming properties of each type of electricity and describe how each property affects the uses of the form of electricity.

• Assign each student one of the vocabulary words from the chapter. (If you have more students than vocabulary words, you can either have students work in pairs or assign students additional key terms from the chapter that were not vocabulary terms.) Have students take photographs, draw images, or find images in magazines or on the Internet to represent their vocabulary words. Once students have found a number of images for their words, ask them to make collages illustrating the meanings of the words.

• Have students complete the questions found in the Chapter Self-Quiz and Chapter Review in the Student Book.

• Have students complete BLM 12.Q Chapter 12 Quiz for an additional review of the material.

DIFFERENTIATED INSTRUCTION • Allow students to demonstrate their mastery of the Key Concepts and

vocabulary in different ways. Verbal/linguistic learners might write a summary of the chapter. Interpersonal learners might give an oral report or create a simulated news interview. Mathematical/logical learners might create graphic organizers or other diagrams.


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LITERACY TIPS AND ENGLISH LANGUAGE LEARNERS • Distribute copies of BLM 0.0-6 Chapter Key Concepts. Ask students to write

one Key Concept on each indicated line, rephrasing the Key Concept in their own words. Then have students summarize all of the Key Concepts. You may need to provide lower-proficiency English language learners with sentence frames or a word bank to help them complete the summaries.

Time 45–60 min Skills Looking Back provides an opportunity for students to demonstrate their

understanding of and their ability to apply the key concepts, vocabulary, and skills.

Literacy Resources BLM 0.0-6 Chapter Key Concepts Assessment Resources BLM 12.Q Chapter 12 Quiz Other Program Resources Science Connections 9 website www.nelson.com/scienceconnections/9


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Chapter 12 Chapter Self-Quiz

SUGGESTED ANSWERS 1. (d)

2. (b) 3. (d) 4. (c) 5. (c) 6. False. Tap water is a good conductor of electricity because it contains

dissolved salts and charged particles. 7. True.

8. False. Computers are shipped in special anti-static packaging to protect against electric discharge.

9. False. Current electricity refers to the movement of electrons in a closed path.

10. True.

11. False. You must ground an object to permanently give it a charge.

12. False. Neutral objects are not attracted to negatively charged objects or positively charged objects.

13. Charging by induction causes electrons in a neutral object to move.

14. Objects with like charges repel each other.

15. An insulator is a material that prevents the flow of current.

16. A rapid release of static energy is an electrostatic discharge.

17. Permanent charging by induction results in two charged objects that have opposite charges.

18. (a) iii; (b) iv; (c) v; (d) ii; (e) vi; (f) i

19. When an object becomes positively charged, some of its atoms lose one or more of their outer electrons, leaving the object with more positive charges than negative charges. The diagram below shows an example.


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20. Sample answer: An excess of static charge can be produced in the oil as it is pumped through the hoses to be emptied. The metal wire connects the tanker car to the ground. Since the metal is a conductor, the wire will allow the charge to discharge and flow safely to Earth instead of a producing a spark (electric discharge) and igniting the fuel.

21. During a storm, particles in clouds become charged by friction. When the charge difference becomes great enough, a spark discharges through the air.

22. (a) Static cling is caused by the attraction between the positive and negative charges the build up on clothes as they tumble against each other in the dryer, charging each other by friction.

(b) When you pull clothes out of the dryer, the crackling sounds are electric discharge (or electrostatic discharge, ESD). As you touch the clothes, the charges discharge through contact with your skin or the metal sides of the dryer.

23. When you take off the wool hat, it rubs against your hair. Electrons move from the hat to your hair. Each hair has the same negative charge. Because things with the same charge repel each other, the hairs repel each other and stand on end away from each other.

24. When the first pith ball is touched by the negatively charged rod, it becomes negatively charged. This pith ball induces a positive charged in the second pith ball, and the two balls attract each other. When they touch, the second pith ball also becomes negatively charged, and the balls repel each other. If the rod is brought near either of the pith balls, it will cause them to repel each other even more since they all have the same charge.

25. The coating is placed around the wire to protect the user from getting an electric shock. The coating is made of an insulator, which resists electron flow. The wire is made of metal, which is a conductor, and this easily allows electron flow, allowing a current to flow in the wire.


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26. (a) A metal leaf electroscope is charged if its two leaves are apart.

(b) To tell whether a material is a conductor or an insulator, first charge the electroscope. Then, bring the material you want to test near the charged electroscope. If the material is a conductor, the charge on the electroscope will discharge and the leaves will fall. If the material is an insulator, there will be no discharge.


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Chapter 12 Chapter Review

SUGGESTED ANSWERS

WHAT DO YOU REMEMBER? 1. (a) An object is electrically neutral if it has an equal number of protons and

electrons.

(b) Charging by induction means charging over a distance without direct contact.

(c) An electrical insulator is a material that resists the flow of electric current through it.

(d) Electrical conductivity is a material’s relative ability to conduct electrons.

(e) Electric discharge is the sudden release of electric charge.

(f) Electric current is the movement of electrons through a material in a closed path.

2. The electrical energy distribution grid consists of a power plant with an electric generator, substations, transmission lines, transformers, and power lines that lead into homes and businesses. The electric current produced at the generator goes through transformers for transmission over long distance lines and is transformed again to safe levels for personal use.

3. Sample answer: Vinyl cling advertising uses static electricity to cling to most clean, smooth surfaces. Photocopiers place an image of the item being copied onto a charged surface that attracts charged particles of toner to it. The image is then transferred to a charged piece of paper.

4. Like charges repel, and unlike charges attract. Electric force weakens with increasing distance between charged objects and gets stronger the closer the charged objects are to each other.

5. Sample answer: Three examples of charging by contact: your hair becoming charged by moving a comb through it, static cling developing on clothes because they rub against each other in a dryer, and a balloon becoming charged when you rub it with wool.


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6. (a) Sample answer:

(b) Sample answer:

(c) Sample answer:

7. The air is filled with molecules of water vapour on a humid day. These molecules attract and draw away some of the charged particles from objects. Such collisions are less frequent when the air is dryer.

8. An insulator holds onto its electrons more strongly than a conductor does. A conductor’s electrons can flow, producing an electric current. An insulator resists the flow of electrons. Current cannot easily flow through it.

WHAT DO YOU UNDERSTAND? 9. (a) Direct current is an electric current that flows through a conductor in one

direction only. Alternating current repeatedly reverses direction.

(b) Sample answer: Direct current is commonly used in radios and flashlights. Alternating current is used in household electric lines to power computers, toasters, TVs, and other electronic devices.


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10. The clothes rub against each other as they tumble in the dryer. Electrons move from one type of fabric to the other, charging the fabrics by friction. One type of fabric is left positively charged and another type is left negatively charged.

11. Static electricity remains at rest until it jumps from one object to another. 12. Protons and neutrons are bound tightly in the

atom’s nucleus, but electrons move around the nucleus and are less tightly bound. The outermost electrons of some materials, such as the aluminum atom shown here, have enough energy to move freely among atoms.

13. Both static electricity and current electricity involve the movement of electrons. In static electricity, charge builds up and then can suddenly discharge. Current electricity flows continually in a closed path.

14. Bringing a charged object near a neutral object induces a charge separation in the neutral object. The charge on the side closest to the charged object is opposite that of the charged object, causing the objects to attract each other.

15. The charged object induces charge separation on the neutral pith ball, and the object and pith ball attract each other. The charged object also induces charge separation on the neutral knob of the electroscope. This causes the metal leaves to have the same charge and repel each other and separate.

16. The negative charge that builds up on the bottom of clouds during a thunderstorm induces charge separation in the nearby ground. The ground surface then is positively charged.

17. When you walk around a room, your body can become charged by friction. A discharge to sensitive electronic circuits can damage them. The anti-static device is grounded to Earth. Excess charge flows harmlessly to Earth instead of building up on your body.

SOLVE A PROBLEM 18. (a) Rubbing the plate with cloth gives it a charge. The charged plate induces

an opposite charge on water molecules and then attracts them.

(b) When the plate gets near the metal rack, there is a sudden electric discharge because the metal is a good electrical conductor.

19. The metal lightning rod is a conductor. Instead of striking other parts of the building, lightning strikes the rod because it has less resistance. The electric discharge will safely move down the rod, along the conducting wire, and into the ground.


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20. (a) The metal spheres are conductors. The balloons and the supporting rods are insulators.

(b) The positively charged balloon is brought near but not touching the first sphere. This induces a negative charge on the surface of the sphere near the balloon. Because the spheres are touching, electrons move from sphere B to sphere A, causing sphere A to be negatively charged and sphere B to be positively charged. When the spheres are separated, the charges cannot move back, and the charges on the spheres are permanent.

21. The negatively charged balloon induced charge separation in the floating bubbles without touching them. The bubbles were then attracted to the balloon, and the student could move the bubbles with the balloon.

CREATE AND EVALUATE 22. Sample answer: Rub a balloon with wool to give the balloon a negative

charge. Bring the balloon near the knob of an electroscope. The knob will be positively charged and the leaves will both be negatively charged and separate. Bring the unknown material near the knob. If the material is positively charged, electrons will move from the electroscope to the material, discharging it, and the leaves will fall. If the material is negatively charged, there will be no effect.

23. Check that students have described how they investigated the effectiveness of several dust-removal products, including explaining the criteria they used to evaluate the products (such as whether any dust remained on surfaces after the product was used and how easily each product removed dust. Also check that students have evaluated the effect each product has on the environment.

REFLECT ON YOUR LEARNING 24. Sample answer: I was most interested in how a photocopier uses static

electricity. I thought it was surprising that such small detail as letters on a page could be attracted so precisely onto a charged drum and then onto the paper by static charge.

25. Sample answer: Yes. I realized how important it is to avoid electric discharge when working around electronic devices. I also realized how easy it is to safely discharge any charge buildup.

WEB CONNECTIONS 26. Check that students have described how maglev trains use magnetic force to

push or pull the train along a path while the train is levitated by the magnetic force just above the tracks. The force required to do this is achieved using electromagnets, which work on the principle that a changing electric field produces a magnetic field. The changing electric field is provided by an alternating current.


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27. Check that students’ presentations describe why electrostatic discharges could be so harmful and explain possible methods considered by NASA to avoid the problems. Also check that students explain that grounding on Mars and the Moon is different because there is no water there as on Earth to dissipate charge. On Mars, the air might be used for grounding; on the Moon, a system might be built to provide a means of grounding.

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