Textbook chapter 1 answers

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Unit

C

Electromagnetic Energy

Lesson Internet Search CD Links Handouts Investigations QuestionsLesson

Chapter Review Questions

Unit Review Questions

Chapter 1: Electric and Magnetic Fields

1.1 3 3 3 3 3 3

1.2 3 3 3 3 3 3 3

1.3 3 3 3 3 3 3

1.4 3 3 3 3 3 3

1.5 3 3 3 3 3 3

Chapter 2: The Electromagnetic Spectrum

2.1 3 3 3 3 3 3 3

2.2 3 3 3 3 3 3 3

Unit Organization Chart

UnIT C: ELECTROMagnETIC EnERgy

note: Students do not have access to the answers for the chapter review questions or the unit review questions.

Overview

This unit consists of two chapters. Chapter 1 introduces electric, magnetic, and gravitational fields. The properties of fields are explored from the point of view of natural phenomena such as lightning and the northern lights. Field lines and equations for fields are introduced next in the context of the challenges of space exploration—a storyline that is picked up again when astronomy is studied in Chapter 2. The remainder of Chapter 1 is more down to Earth as electric and magnetic fields are applied to motors, generators, and electric circuits and to the transmission of electrical energy. This chapter is rich in student activities that provide students with many meaningful learning experiences.

Chapter 2 continues the work with electric and magnetic fields by introducing students to the electromagnetic spectrum. After a quick introduction to electromagnetic waves, students complete a survey of all the regions of the electromagnetic spectrum. Many links are made to key ideas from previous units as students see how electromagnetic radiation relates to living systems and to the environment. In the second half of this chapter, students investigate some of the properties of electromagnetic radiation. These properties are applied to the devices and techniques used by astronomers to study celestial objects.

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Unit

C

Electromagnetic Energy

attitude Outcomes

The major attitude outcomes for this unit are interest in science and scientific inquiry. This unit features many technologies that are highly relevant to students: headphones used in portable sound systems, small motors, and remote controls, to name a few. These devices have been incorporated into investigations so that student interest in these products can become a strong motivator for probing the underlying concepts.

Another key attitude outcome addressed in this unit is safety. Given that electricity is used extensively in this unit’s investigations, it is important to make students aware of the proper procedures for the safe use of electricity. This must be tempered with the notion that students should be encouraged to develop the confidence to properly use devices such as voltmeters and ammeters in the lab. These attitudes can be extended to events in the students’ lives outside of the classroom, where electrical devices are used at home and in the workplace. Safety is also featured as students explore the nature of the electromagnetic spectrum. Minimizing personal exposure to ionizing radiation is a strong theme in Chapter 2. As was the case with working with electrical equipment in Chapter 1, it is important that students balance caution with the confidence that comes from being well-informed, scientifically literate citizens. Beyond this course, students will encounter electromagnetic radiation in a number of devices and in a variety of circumstances, so it is important that they move beyond the misconceptions regarding radiation that are perpetuated by popular culture.

Many students may not have worked with electrical devices since Grade 9 Science. The investigations play a key role in developing all of the attitude outcomes for this unit. Participation in these activities is a great way to foster interest in science and skills related to scientific inquiry. The investigations are also a great way to provide hands-on experiences so that students can learn to use equipment safely and effectively.

Preparation for Unit C

Due to the mathematical nature of this unit, students may find it to be a challenge. For many students, their struggles with mathematics played a significant role in their decision to take Science 30 as opposed to

Chemistry 30 or Physics 30. Given this trend, it is essential that you are consistent in the way that you present mathematical solutions. A clear, consistent approach allows each worked example to become a benchmark, communicating the course standards to students. Students are expected to be able to rearrange a simple equation, such as N_p/N_s=V_p/V_s, for any one of the variables. It is crucial to provide as many opportunities as possible for students to practise this so that they can improve their abilities.

It is recommended that you discuss these issues with colleagues teaching other mathematics and science courses prior to teaching this unit. Your students will appreciate it if your methods are complementary to what they do in other courses.

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Handouts for Unit C

The following handouts are provided for Unit C. The student handouts are on the Science 30 Textbook CD. The teacher handouts are on the TRG CD.

Chapter 1 Lesson 1.1

Student Handouts

• “Placement of a Compass Around a Bar Magnet” (pp. 322, 323) • “Observing Electric Fields: Sources” (p. 325)

• “Observing Electric Fields: Lightning Safety” (p. 325)

Teacher Handouts

• “Building a High-Voltage Power Supply”

Lesson 1.2

• “Plotting the Gravitational Field Strength of Venus” (p. 332) • “Magnetic Field Surrounding a Small Coil” (p. 340)

• “Labelling the Magnetic Field Around a Current-Carrying Coil” (p. 343)

• “Labelling the Magnetic Field Around a Current-Carrying Coil—Labelled”

Lesson 1.3

• “Building the Armature” (p. 352) • “Building the Stationary Parts” (p. 352) • “Motor Analysis” (p. 360)

• “Motor Dissection” (p. 360)

• “Properties of DC and AC Generators” (p. 361) • “Disassembling Inexpensive Headphones” (p. 363)

• “Properties of DC and AC Generators—Labelled”

Lesson 1.4

• “Multimeter Troubleshooting” (p. 369)

• “Symbols for Components in Schematic Diagrams” (p. 373)

Lesson 1.5

• “Generating Electricity with Fossil Fuels” (p. 403)

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Chapter 1 Review Questions

• “Sketching Fields” (p. 405)

• “Generating Electricity with Fossil Fuels” (p. 408) • “An Energy-Conversion Device” (p. 409)

• “Sketching Fields—Labelled”

Chapter 2 Introduction

• “Properties of the Waves Emitted by Remote Controls” (p. 411)

Lesson 2.1

• “Electromagnetic Energy to Electrical Energy” (p. 415) • “Building an Infrared Transmitter and Receiver” (p. 425)

• “Questionnaire: Estimating Your Annual Dose of Ionizing Radiation” (p. 433) • “Summarizing the Characteristics of the Electromagnetic Spectrum” (p. 434)

• “Electromagnetic Energy to Electrical Energy—Labelled”

• “Summarizing the Characteristics of the Electromagnetic Spectrum—Labelled”

Lesson 2.2

• “Investigating Refraction” (p. 441) • “Investigating Polarization” (p. 441) • “Investigating Diffraction” (p. 441) • “Investigating Reflection” (p. 441)

• “Tracking Space-Based Telescopes and Other Satellites” (p. 446) • “Observing Continuous and Emission Spectra” (p. 449)

• “Summarizing Multiwavelength Astronomy” (p. 455) • “Reference Absorption Spectra” (p. 455)

• “Observing Continuous and Emission Spectra—Labelled” • “Summarizing Multiwavelength Astronomy—Labelled”

Chapter 2 Review Questions

• “Reference Absorption Spectra” (p. 459)

Unit C Review Questions

• “Reference Absorption Spectra” (p. 462)

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Safety Considerations for Unit C

Chapter 1 Lesson 1.1

The “Observing Electric Field Lines” investigation requires students to use a high-voltage power source to produce electric field lines in a Petri dish filled with mineral oil. The high-voltage power source is capable of giving students an uncomfortable electric shock that is similar to the shock they could get from a van de Graaff generator. Since it is important that students be aware of the proper procedure for using this equipment, the technique described in the textbook is worth demonstrating. Clearly, the maturity level of the students needs to be consistent with the expectations of this activity.

Note that an inexpensive high-voltage power source can be built by modifying an electronic bug zapper. Detailed instructions are provided in the “Building a High-Voltage Power Supply” handout. As in the procedure for the investigation, if you have student volunteers build several of these devices, it is important to demonstrate the assembly procedures yourself and then to carefully supervise the students.

Lesson 1.2

The “Using a Coil to Deflect an Electron Beam” activity involves students making momentary contact with a four-cell battery pack so that an electric current can flow through a small, handmade coil of wire. If the electric current is allowed to flow for more than the few seconds it takes to make the observations, the coil can become uncomfortably warm. Students should be alerted to this possibility and should be encouraged to allow the current to flow for the shortest time interval possible.

Lesson 1.3

In the “Building an Electric Motor” activity, students build a simple electric motor that is powered by a four-cell battery pack. If electric current from the battery pack is allowed to flow through the coil of the armature when the armature is not turning, the coil can become uncomfortably warm. Students should be alerted to this possibility and encouraged to maintain contact for only a few seconds at a time while troubleshooting.

Lesson 1.4

In the “Comparing Two Ways of Determining Resistance” investigation, students will be using a digital multimeter to make a number of measurements for an electric circuit.

The following safety warnings (which are given in the textbook) should be brought to the students’ attention, particularly if they are using a low-voltage power supply that plugs into an AC wall outlet:

• Never ground yourself while working with a live circuit. Do not touch metal pipes, electrical outlets, light fixtures, etc., that might be grounded. Be sure to keep your body insulated by keeping your hands and body dry and by wearing dry clothing and running shoes.

• Replace the fuse inside the meter with only the specified or approved equivalent fuse. Fuse replacement should only be done by the teacher or an adult lab technician.

• Use the meter only as specified in the investigation. Do not use the meter to test a wall outlet or an electric appliance. If you try to measure a voltage that exceeds the limits of the meter, you may damage the meter and expose yourself to serious electric shock.

• Resistors can become warm—in some cases, hot enough to cause burns. Always disconnect a recently used

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Lesson 1.5

The “Exploring the Transformer” activity involves students making momentary contact with a four-cell battery pack so that an electric current can flow through a small, handmade coil of wire. If the electric current is allowed to flow for more than the few seconds it takes to make the observations, the coil can become uncomfortably warm. Students should be alerted to this possibility and should be encouraged to allow the current to flow for the shortest time interval possible.

Chapter 2 Lesson 2.2

In parts of the “Observing the Properties of Visible Light” investigation, students have the option of using a ray box or a small laser pointer to produce rays of light. If students are using a laser pointer, it is important to ensure that they follow all the recommended safety precautions so that laser light does not enter a student’s eyes. The following specific safety information is given in the textbook.

Mandatory Safety Precautions for Working with Laser Light

• Never aim a laser at a person’s eye.

• Avoid having the unprotected eye along or near the beam axis.

– If you are working at a table, this means keeping the laser light parallel to the surface of the table so that your eyes are well above the work surface.

– Anticipate the path the laser light will take and arrange the apparatus so that the beam will not inadvertently be directed near the eyes of other students. One useful strategy is to work around the

perimeter of the room, with the laser light directed toward the outside wall. This arrangement also ensures that your eyes are facing away from other groups.

• Keep the room well-lit so pupils remain small, reducing the “window” available for the entry of laser light.

• Avoid having the laser produce light for extended periods of time. Once the apparatus is in place, most measurements or observations can be made in a matter of seconds; then the laser can be switched off.

In the “Observing Spectra” activity, a high-voltage power source is used to operate the gas-discharge tubes that produce the various spectra. The source of electrical energy presents a significant shock hazard if the electrodes are accidentally touched when the source is switched on. The gas-discharge tubes can also become hot. For these reasons, it is recommended that students not be allowed to exchange the discharge tubes for individual gases in the power supply.

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Materials for Unit C

The Science Data Booklet and computer access are required throughout the unit.

Quantities given are the amount needed for each station where an individual or small group will work.

Chapter 1 Introduction

Try This Activity: Observing Magnetic and Electrical Effects

• bar magnet

• 3-inch common nail • ebonite rod and fur

• pith ball • 1 m of thread • retort stand and utility clamp • tape

Lesson 1.1

Investigation: Observing Magnetic Field Lines

• ceramic or iron bar magnet

• iron filings in a container with a removable lid that allows the filings to be sprinkled • compass

• lid of a shoebox with one end open

• cookie sheet that is ferromagnetic (A magnet will stick to it.)

• two books that are the same thickness (Both must be thicker than the bar magnet.)

• “Placement of a Compass Around a Bar Magnet” handout from the Science 30 Textbook CD

Investigation: Observing Electric Field Lines

• high-voltage DC power supply (at least 500 V DC) • large Petri dish (100 mm by 15 mm)

• 200 mL of mineral oil • 10 mL of grass seed

• variety of objects to become charged in the Petri dish – straight-line sources (1

2-inchcopper plumbing tees)

– point sources (3

4-inchcopper plumbing coupling)

– variable-shaped sources (large hex nuts or eyebolts)

– 2 strips of thin metal sheeting (2 cm by 15 cm each) (inexpensive metal flashing used for roof repair) • latex or vinyl gloves

• waste bucket to recover mineral oil

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Lesson 1.2

Investigation: Using a Coil to Deflect an Electron Beam

• 1 cardboard cylinder about 4 cm in diameter and 10 cm in length (empty toilet-tissue roll) • 10 m of 26- or 28-gauge enamelled magnet wire

• 4 AA cells in a plastic battery pack • 2 test leads with alligator clips at each end

• access to an operating CRT monitor (conventional TV or computer monitor) • small knife or 1 piece of fine sandpaper

• tape • compass

• “Magnetic Field Surrounding a Small Coil” handout

Lesson 1.3

Investigation: Building an Electric Motor

• 4 AA cells in a plastic battery pack with leads • 3, 5.0-cm bolts

• 2 test leads

• 2, 0.50-m pieces of solid, insulated 20-gauge connecting wire • block of wood (3.5 cm by 9 cm by 30 cm)

• 2 metal angle brackets with predrilled holes (each side about 5.0 cm long) • 2 metal angle brackets with predrilled holes (each side about 6.3 cm long) • 4 wood screws (about 5.0 cm long)

• 4 hex nuts ( 7

16-inchthread size)

• 6 ceramic disc magnets (about 1.8 cm in diameter and 1 cm thick)

• piece of wood dowelling (about 6 mm in diameter and exactly 20.0 cm long) • 5 m of 26-gauge enamelled magnet wire

• cylindrical glassware with a diameter of 3–4 cm • 2 straight pins (2.5 cm long)

• 4 m of black thread • 10 small paper clips • ring stand

• large “bulldog” paper clamp • transparent adhesive tape • sharp knife

• wire cutters • wire strippers • pliers

• screwdriver

• digital multimeter or a voltmeter • scissors

• fine sandpaper

• “Building the Armature” handout • “Building the Stationary Parts” handout

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Investigation: Connections Between Headphones and Motors

• set of headphones that are efficient (capable of reproducing loud sound at low volume) • inexpensive set of headphones to be disassembled

• access to a computer with speakers and a microphone input • 4 AA cells in a plastic battery pack

• 2 test leads • digital multimeter • small slot screwdriver • probe from a dissection kit

• portable music system (CD player, MP3 player, radio) • “Disassembling Inexpensive Headphones” handout

Lesson 1.4

Try This Activity: Building Simple Circuits

• 4 AA cells in a plastic battery pack • 4 test leads

• 2 mini light bulbs with bases

Investigation: Comparing Two Ways of Determining Resistance

• digital multimeter

• 3 resistors (1000 W, 1500 W, and 2000 W)

• low-voltage power supply or 4 AA cells in a plastic battery pack with 3, 50-mm screws

Try This Activity: Maximum and Minimum Resistance

• 3 resistors (1000 W, 1500 W, and 2000 W) • digital multimeter (used as an ohmmeter) • test leads

Lesson 1.5

Investigation: Exploring the Transformer

• 4 AA cells in a plastic battery pack with leads • digital multimeter

• cardboard cylinder about 4 cm in diameter and 10 cm in length (empty toilet-tissue roll) • 2, 10-m pieces of 26- or 28-gauge enamelled magnet wire

• 4 test leads with aligator clips at each end • strong bar magnet

• iron rod from a ring stand • small knife

• adhesive tape

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Chapter 2 Introduction

Try This Activity: Exploring Coded Signals

• photovoltaic cell with two leads

• 2 test leads with alligator clips at each end

• pair of sensitive headphones (the type you might use with a portable music system) • at least two different remote controls, preferably with different brand names • “Properties of the Waves Emitted by Remote Controls” handout

Lesson 2.1

Investigation: Electromagnetic Radiation Transfers Energy

• overhead projector set up with an equilateral prism by your teacher • photovoltaic cell with two leads

• 2 test leads with alligator clips at each end • digital multimeter

• “Electromagnetic Energy to Electrical Energy” handout

Investigation: Building and Testing an Infrared Transmitter and Receiver

• portable music system with a headphone jack (e.g., CD player or MP3 player) • set of sensitive headphones (the type you would use with the portable music system) • 7 test leads with alligator clips at each end

• 7 small elastic bands to shorten the test leads • 1 AA cell in a holder with leads

• photovoltaic cell with leads

• infrared LED (light-emitting diode) with peak wavelength of 940 nm • 0.22-µF capacitor (50 WVDC max)

• audio cable with 3.5-mm (1

8-inch) stereo plugs at each end (must be less than 2 m long)

• infrared remote control • 6 sheets of facial tissue

• “Building an Infrared Transmitter and Receiver” handout

Lesson 2.2

Investigation: Observing the Properties of Visible Light

This investigation has four parts, each with its own materials list.

• Investigating Reflection

– ray box or a small laser pointer

– small mirror or flat piece of shiny metal

– small piece (2 cm by 30 cm) of shiny metal that is flexible enough to be bent into a curve

• Investigating Refraction

– ray box or a small laser pointer – D-shaped dish that can hold water – D-shaped block of glass

– about 300 mL of water

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• Investigating Polarization

– coin

– pair of polarized sunglasses – 2 polarizing filters

– shallow bowl

– about 300 mL of water

• Investigating Diffraction

– light source (60-W bulb on a lamp stand with the shade removed) – 2 pieces of thin cardboard (from a large breakfast cereal box)

– 40 cm by 30 cm (used as a cardboard shield with two tiny pinholes) – 5 cm by 10 cm (used to make the circular disks for the pinhole viewer)

– cardboard cylinder about 4 cm in diameter and about 10 cm long (empty toilet-tissue roll) – adhesive tape

– small pin or sewing needle that is less than 0.5 mm in diameter – large pin or sewing needle that is about 2 mm in diameter – scissors

– 2 ring stands

Try This Activity: Seeing the Invisible

• digital camera

• infrared remote control

Investigation: Observing Spectra

• handheld spectroscope

• high-voltage power supply that can run gas-discharge tubes

• gas-discharge tubes for different gases (hydrogen, helium, mercury, and neon) • showcase light bulb mounted in a lamp with a dimmer switch

• standard fluorescent tube light source (often used as ceiling lighting for classrooms and kitchens) • coloured pens or pencils

• “Observing Continuous and Emission Spectra” handout

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UnIT C: ELECTROMagnETIC EnERgy

Lesson Knowledge Outcomes OutcomesSTS OutcomesSkill OutcomesICT

1.1 30-C1.1k

30-C1.2k 30-C1.3k

30-C1.2s C6-4.4

1.2 30-C1.3k

30-C1.4k 30-C1.12k

30-C1.2s 30-C1.3s

C3-4.2 C6-4.1 C6-4.3 C7-4.2 P2-4.1

1.3 30-C1.5k

30-C1.8k 30-C1.11k

30-C1.1sts 30-C1.2sts

30-C1.2s 30-C1.3s 30-C1.4s

F2-4.3 F2-4.8 F3-4.1

1.4 30-C1.6k

30-C1.12k

30-C1.1sts 30-C1.1s

30-C1.2s 30-C1.3s

C6-4.4 C6-4.5

1.5 30-C1.7k

30-C1.9k 30-C1.10k 30-C1.12k

30-C1.1sts 30-C1.2sts

30-C1.3s F2-4.8

F3-4.1

2.1 30-C2.1k

30-C2.2k 30-C2.4k 30-C2.5k

30-C2.1sts 30-C2.3sts

30-C2.1s 30-C2.3s

C6-4.4 F2-4.3 F2-4.4 F3-4.1

2.2 30-C2.3k

30-C2.4k 30-C2.6k 30-C2.7k 30-C2.8k 30-C2.9k 30-C2.10k 30-C2.11k

30-C2.1sts 30-C2.2sts 30-C2.3sts

30-C2.1s 30-C2.2s 30-C2.3s 30-C2.4s

C2-4.1 C2-4.2 C3-4.1 C3-4.2 F2-4.2 F2-4.7 F2-4.8 F3-4.1

Program of Studies Correlation Chart

general Outcomes

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Chapter 1: Electric and Magnetic Fields

This chapter introduces students to the concept of a field. A field is a property of the space surrounding a mass, an electric charge, or a magnet that enables each of these objects to exert a force on a test body introduced into this region. Historically, the phrase “action at a distance” has been used to describe situations in which a source object is able to exert a force on a test body without any apparent physical contact between the two objects. Forces that demonstrate this property include gravity, electricity, and magnetism. The notion of a field is subtle and may be challenging for students to grasp.

The approach taken for these topics is quite different from a traditional high school physics textbook. Both the number of equations and the number of calculations are reduced in comparison to the traditional approach. The emphasis here is more on connections between these concepts and those from other units, as well as applications to technologies.

When you are helping your students with calculations, they will find it helpful if you clearly distinguish between the source of a field and the test body that experiences the force. This is important because some equations require students to substitute a value for a source, while others require a value for a test body. Consistently using the words source and test body will help your students keep all this straight.

By the third lesson, the emphasis switches from the application of fields to natural phenomena to applications involving technologies. The investigations and activities throughout Chapter 1 are central to the development of the concepts within the lessons. If you are unable to have your students complete an investigation or activity, one option is to turn it into a demonstration.

Try This activity: Observing Magnetic and Electrical Effects, page 311

This activity gives students hands-on experience with two fundamental forces: electricity and magnetism. Although the students have yet to be introduced to the term field, you can use the students’ experiences with this activity to reinforce a key point later in the chapter: these forces are all “action-at-a-distance” forces, as opposed to contact forces, like the force of friction. You could ask your students the following focusing question at the end of this activity: Since action-at-a-distance forces do not require physical contact between two objects, how can a force be exerted by one object on another if they do not touch? The rest of the chapter centres around the answers to this fundamental question.

One tricky aspect of the procedure for this investigation occurs in steps 2, 7, and 9. In these steps, an ebonite rod or a magnet is brought close to the suspended object, but it is not allowed to touch it. This is not an easy task because the suspended object will tend to suddenly move and attempt to make contact when the distance of separation is small. Keeping the test object slightly below the horizontal plane of the suspended object may prove helpful.

analysis

1. Both magnetic and electrical effects are similar in that they can involve the attraction and repulsion of other objects. One difference between the effects is that the ebonite rod required preparation (was rubbed with fur) prior to its use in demonstrating electrical effects. The bar magnet required no such preparation.

2. Although answers to this question will vary, many students may communicate the idea of some kind of connection between the source and the test body. Answers could include phrases like “the electricity is able to travel through the air.” Other students may attempt to make connections to related phenomena, such as lightning travelling from a cloud to the ground or a compass needle being affected by Earth.

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This lesson uses the context of lightning and safety to introduce the concept of fields. The ideas of

measuring charge in coulombs and voltage in volts is introduced to help provide the necessary background information for the descriptions of lightning and for the last investigation in the lesson. The electric field is introduced as a property of the space surrounding the negative charges that collect on the bottom of a thundercloud. This negative charge is the source of an electric field. Test bodies include frayed threads on the jackets of the hikers and possibly the hairs on their heads.

The notion of a field emanating from a source that can exert forces on test objects is used to develop the concepts of magnetic fields and gravitational fields. It is important to stress the nature of the source and the properties of the test body for each type of field.

Type of Field general Description of Sources for This Field Test Bodies for This Fieldgeneral Description of

electric

Source objects are either positively or negatively charged.

Test bodies for electric fields are small charged objects. The direction of the electric field is defined as the direction of the electric force on a positive test charge.

magnetic

Source objects are either magnets or electric currents.

Test bodies for magnetic fields are small magnets, such as compass needles.

gravitational

Source objects have mass. Test bodies for gravitational fields are small objects with mass.

Although these ideas will be elaborated upon in the next lesson, it is important to establish a good foundation here.

The lesson ends with the introduction of field lines as a way to describe the direction and the intensity of fields. The investigation “Observing Magnetic Field Lines” is straightforward and involves equipment that is readily available. Many teachers have likely completed variations of this investigation while teaching previous courses.

The last investigation, “Observing Electric Field Lines,” is more challenging because it is likely a new experience for the teacher and because it requires quite a bit of preparation in terms of equipment. Teachers may choose to do this investigation as a demonstration if they are unable to complete it as a student lab investigation.

Teaching Strategies

Lesson 1.1: Field Lines

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Practice, page 314

1. The path of lightning is determined by pockets of ionized air molecules in the atmosphere. Since the air pockets are not evenly spaced and are randomly distributed, the path of the lightning strike is not a straight line. Instead, lightning strikes are jagged, following the pockets of ionized air molecules.

2. a. If the air has a high moisture content, it will release more energy as water vapour condenses into droplets. The added energy has the effect of heating up the parcel of air, which causes it to rise even higher.

b. A rising column of water vapour rushes past a column of descending water droplets. Since water molecules in the droplets hold onto their electrons more tightly than water molecules in the vapour, the water droplets become negatively charged by collecting electrons from some of the water molecules. As the droplets fall, the bottom of the cloud becomes negatively charged and the top of the cloud becomes positively charged.

3. a. Since the ebonite rod gained electrons, it is said to be negatively charged.

b. q_rod electrons C electrons C

= ¥ ¥ ¥ = ¥

-1 4 -10 1 00

6 25 10 2 2 10

10

18

9

. .

The ebonite rod would have a charge of - 2.2 ¥ 10- 9_{C. Note that the charge on the rod is negative since}

the rod gained electrons.

Practice, page 316

4. a. q

V

E

=

= ¥ D =

15

1 50 108

C

V

p

.

?

V E

q E Vq

= D

D =

=

(

¥

)

(

)

= ¥

p

J/C C J

1 50 10 15 2 3 10

8

9

. .

The lightning strike delivered 2.3 ¥ 109_{J of energy.}

b. The value of the electrical energy delivered by the lightning strike in question 4.a. is nearly 80% of the value of the total electrical energy used by a typical Alberta home in one month. Although these energy values are very similar, a key difference is that the energy in a lightning strike is delivered in a fraction of a second, while the electrical energy used by the house is used over one full month.

Practice, page 321

5. a. Trees and ridges project into the air and are likely locations for lightning strikes. In an open field, a hiker could be the highest point and, therefore, a potential target for a lightning strike.

b. The hikers are illustrated in an area of low ground and are shown sitting down to avoid making themselves part of the shortest path for the lightning. Additional precautions include sitting on their packs and

keeping metal gear away from their bodies. These precautions help reduce the possibility of a hiker becoming part of the conducting path.

6. When a compass is used to determine direction, the only influence on the magnetic compass needle should be Earth’s magnetic field. Objects containing iron, cobalt, and nickel could influence the compass needle in a way that causes it to give an inaccurate reading.

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7. The peak of a mountain is farther from the centre of Earth than the base of the mountain, so the gravitational field lines are slightly farther apart at the peak than at the base. The low concentration of gravitational field lines at the peak indicates that the gravitational field is weaker at this location.

8.

Investigation: Observing Magnetic Field Lines, pages 322 and 323

This investigation involves materials that are familiar to most teachers and students. Nevertheless, it is still worthwhile to remind students not to be careless with the sprinkling of the iron filings. The filings are very difficult to remove from magnets and they can leave permanent stains on clothing. It is also a good idea to remind students not to leave compasses sitting close to magnets for extended periods of time.

Part a: Using Iron Filings as Test Bodies

analysis

1. Magnetic fields are completely invisible. Magnetic field lines can only be indirectly observed through their effects on test bodies.

2. a. By observing patterns of the iron filings, the magnetic field lines appear to be most concentrated near the ends of the bar magnet.

N S

Type of Field

general Description of

Sources for This Field

general Description of Test Bodies for

This Field Source for This Field Two Examples of a

electric

Source objects are either positively or negatively charged.

Test bodies are small charged objects.

• the negative charge on the bottom of a thundercloud • the metal grid on a bug

zapper

magnetic

Source objects are either magnets or electric currents.

Test bodies are small magnets, such as compass needles.

• a current-carrying coil in a speaker

• a fridge magnet

gravitational Source objects _{have mass.} Test bodies are small _{objects with mass.} • Earth • the Sun

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b. The iron filings near the end of each magnet look like miniature spruce trees growing from the surface of the cardboard. In addition, the filings at each end of the magnet seem to follow patterns in terms of the angle that they make to the surface of the box and in terms of their height above the box. These observations support the idea that magnetic field lines form three-dimensional patterns.

3. a. The cookie sheet dramatically reduced the clarity of the patterns formed by the filings. Although the same general shapes could be observed, the patterns were indistinct. The ability of the filings to be lifted above the surface of the cardboard was reduced.

b. If a magnet can stick to a sheet of metal, the metal is called ferromagnetic. The observations described in question 3.a. suggest that a sheet of ferromagnetic metal is somehow able to absorb magnetic field lines, preventing them from passing from one side to the other. This means that a sensitive electronic device could be protected from the influence of magnetic fields by putting the device in a box made of ferromagnetic metal.

Part B: Using a Compass as a Test Body

analysis

4. The south end of the bar magnet attracts the north-pointing end of the compass, and the north end of the bar magnet repels the north-pointing end of the compass.

5.

N S

Utilizing Technology: Two Magnets, page 324

This is a very concise activity that uses computer animation to help students internalize the three-dimensional nature of magnetic fields. This activity would make a wonderful homework assignment once students have completed the “Observing Magnetic Field Lines” investigation.

Summary

The following four statements summarize the key ideas in this activity:

• Arrows are used to represent magnetic field lines.

• Magnetic field lines coming from the north pole to the viewer are represented as dots.

• Magnetic field lines leaving the north pole, going away from the viewer, are represented as Xs.

• Magnetic field lines are only symbolic representations since they are invisible to the eye. The only way to

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Investigation: Observing Electric Field Lines, pages 324 and 325

This investigation requires a considerable amount of preparation and planning on the part of the teacher.

Nevertheless, this is a unique learning experience for students because they can observe test bodies aligning along electric field lines.

Given the other constraints put on a teacher’s time, an alternative approach is to do this activity as a teacher-led demonstration instead of as a student lab investigation. In this case, a video camera and monitor would be essential because the apparatus is so small.

Since most schools do not have a high-voltage DC power supply, it will probably be necessary to build one from an inexpensive, handheld, battery-operated bug zapper. This process is illustrated in the “Building a

High-Voltage Power Supply” handout. Note that this process requires a couple pairs of pliers, some electrical tape, and a screwdriver that matches the screws in the handle of the bug zapper. It is important to remove the batteries and to ensure that the grid is fully discharged before you begin your work. Ensure the grid has been discharged by making contact between the two grids while holding onto the insulated handle of the screwdriver.

Once the power supply is built, you should go through the procedure yourself. The following suggestions are helpful:

• Mineral oil is messy. Once a trial has been concluded, dump the mineral oil into an empty waste bucket; then wipe any remaining grass seeds from the Petri dish with paper towel.

• Add only the minimum amount of grass seed for each trial.

• Once the grass seed has been added, repeatedly switch the high-voltage power supply off and on to help establish the pattern of the electric field.

analysis

1. Electric fields are invisible. The only way to study an electric field is to observe the effects of the field on test bodies. Without test bodies, electric fields would be completely undetectable.

2. The sources that produced evenly spaced electric fields were the straight-line sources. When two straight-line sources were used, the field lines tended to be more regularly spaced, indicating that the intensity of the electric field was uniform in the space between the sources.

The sources that produced concentrated patterns of field lines were the smaller sources and those that had sharp points or projections. This was especially noticeable with the strip of thin metal that was bent into the shape of the ground under the thundercloud. The field lines were most concentrated at the tips of the sharp projections.

3. The charges delivered in a lightning strike move along field lines, just as was observed with the grass seeds. The safest locations in a thunderstorm are those that have the lowest concentration of field lines—in natural depressions farthest from the cloud. In this area, the field lines are the least concentrated, so this is a location where lightning is least likely to strike.

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1.1 Questions, pages 326 and 327

Knowledge

1. a. An object has a negative charge if it has more electrons than protons. This is usually created by the object gaining excess electrons from some other object.

b. An object has a positive charge if it has fewer electrons than protons. This is usually created by the object losing electrons to some other object.

c. A coulomb is an SI unit for charge, where one coulomb is equivalent to the transfer of 6.25 ¥ 1018_electrons.

d. Electric potential difference is the change in potential energy per unit of charge.

e. Voltage is another term for electric potential difference.

f. A volt is a unit for voltage, where 1 V = 1 J/C.

g. An electric field is a property of the space around a source charge that enables the source charge to exert forces on other charges that enter this region.

h. A magnetic field is a property of the space around a magnet or an electric current that enables the magnet or electric current to exert forces on other magnets, such as compass needles, that enter this region.

i. A gravitational field is a property of the space around a source mass that enables the source mass to exert forces on other masses that enter this region.

j. A test body is an observable object that can experience a force due to the presence of a field. The nature of the test body is matched to the type of field that it is able to detect—small masses are the test bodies for gravitational fields, small charges are the test bodies for electric fields, and tiny magnets (like compass needles) are the test bodies for magnetic fields.

k. Field lines are a pattern of lines that describe the direction of a field by the way they point and the strength of a field by their density.

2. Electric, magnetic, and gravitational fields have the following characteristics in common:

• A source object is able to exert a force on a test object without any physical contact. • The field can be described in terms of field lines.

• The fields are invisible.

Electric, magnetic, and gravitational fields have the following differing characteristics:

• The sources and test objects for each field differ. Electric, magnetic, and gravitational fields involve interactions between objects that have charge, magnetic poles, and mass, respectively.

• The field lines for each type of field form different types of patterns.

– Electric field lines can point toward or away from a source, depending upon the nature of the source charge. – Magnetic field lines form loops that are directed from the north pole to the south pole.

– Gravitational field lines always point toward the source.

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3. Fields are completely invisible. They can only be observed indirectly through their effects on matter. The particular characteristics of the matter that allow a field to be observed define the characteristics of the test body for that field. Test bodies for electric, magnetic, and gravitational fields have charge, magnetic poles, and mass, respectively.

applying Concepts

4. a. and b.

bar magnet

N S

magnetic field

Earth’s moon

gravitational field

positively charged

sphere

electric field

negatively charged

balloon

electric field

two charged plates

electric field

+ + + + + + + + + + +

– – – – – – – – – – –

electric field

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5. a. Since the child lost some of the electrons from her body to the plastic material of the playground slide, she became positively charged, while the slide became negatively charged.

b.

c. The voltage developed as a child goes down a slide is a large value—over 20 000 V. This means that 20 000 J of energy are stored for every coulomb of charge that is transferred between the child and the slide. The fact that not many coulombs of charge are transferred means that the total energy is relatively small—large enough to give an unpleasant shock, but not large enough to be life-threatening.

Lesson 1.2: Equations for Fields

electric field lines

The main topic of this lesson is space exploration and the need to protect astronauts from particle radiation during extended missions in space. More specifically, this lesson contains an examination of NASA’s plans to use the Moon as a staging area for other space missions and NASA’s proposal to provide shielding for the astronauts who may be working for extended periods of time on this lunar base. Links are established to Unit A as students are introduced to the hazards presented by cosmic rays and solar wind.

Links to Lesson 1.1 are established as the gravitational field is reintroduced in the context of travelling from Earth to the Moon. An equation for gravitational field strength is introduced. Students are coached through calculations of both the gravitational field strength of a source and the resulting gravitational force on a test body. Students tend to find this challenging because of the mathematical nature of this work and because there is a need to be very clear about which mass is the test mass and which mass is the source mass. As was the case in Lesson 1.1, it is important to be consistent in your communication and to encourage students to use the terms source mass and test mass. Initially, you may want to include the words source and test as subscripts for mass in the equations until students begin to internalize this distinction. This approach was used in the example problems.

The inverse-squared nature of the equation for gravitational field strength is explored in the “Plotting the Gravitational Field Strength of Venus” activity. Students should be able to explain the shape of a

g-versus-r graph by referring to the fact that r is in the denominator of the equation and r is squared. It is not an expectation of the program that students should be able to use ratios of r values combined with the inverse-squared patterns to routinely solve quantitative problems.

Teaching Strategies

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The equation for electric field is developed using a parallel development to the one used for the gravitational field equation—the field equation is introduced, followed by the force equation, and then problems that provide students with practice. The key difference between electric and gravitational fields is direction. Electric fields can be directed toward or away from a source because the direction is determined by the direction of force on a positive test charge. Since gravity is always an attractive force, the direction of gravitational fields is towards the source mass.

The moon base context is also used to introduce magnetic fields. NASA’s plans to deflect the negatively charged particles that bombard the Moon calls for the use of elevated coils of wire that each carry a large electric current. The investigation “Using a Coil to Deflect an Electron Beam” allows students to plot the magnetic field surrounding a current-carrying coil. It also provides an opportunity for students to see how the magnetic field of a coil is able to deflect the electron beam of a TV. Although this investigation takes two full pages to provide detailed instructions, if the procedure is first demonstrated to students, it can be done in less than 30 minutes. The results of the investigation are applied to Earth’s magnetic field, to shielding astronauts on the Moon, and to the northern lights.

Note that Science 30 does not use hand rules or equations to describe magnetic fields. Nevertheless, there is still sufficient challenge in this lesson for students, as many will likely find this lesson to be one of the most challenging lessons in this unit.

Practice, page 329

9. A positively charged particle would tend to attract electrons that are held by molecules. In some cases, the electrons could be removed from a covalent bond between two atoms within the molecule, causing the chemical bond to break and the structure of the molecule to change.

10. As you learned in Unit A, the DNA molecule consists of two strands of nucleotides. The strands are said to be complementary because the phosphate base in a nucleotide on one strand will only bond with a certain base from a nucleotide on the other strand. Complementary base pairings for DNA are adenine with thymine and cytosine with guanine.

If a fast-moving charged particle damages an adenine base on one strand of DNA, there is only one way for the cell to repair this damage because the thymine base on the other strand will only bond with a replacement adenine base. However, if an ionized particle breaks both strands, the blueprint for an accurate repair has been destroyed. If the cell randomly adds the same number of bases that were destroyed by the ionized particle, the result could be a point mutation. If the cell attempts a repair by simply rejoining the broken strands without substituting for the destroyed bases, the result is a more serious frameshift mutation. As you learned in Unit A, mutations such as these can cause the death of the cell or can lead to diseases such as cancer.

Utilizing Technology: Plotting the gravitational Field Strength of Venus, page 332

This activity utilizes the capabilities of a graphing calculator to allow students to probe the properties of the inverse-squared relationship between the gravitational field strength and the distance from the centre of Venus. Students will use the table capabilities of their graphing calculators.

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Procedure

1. The completed table and graph are shown.

Trial

Distance from Centre of Venus

( ¥106_m)

gravitational Field Strength

(n/kg)

1 8.00 5.08

2 10.0 3.25

3 12.0 2.26

4 14.0 1.66

5 16.0 1.27

6 18.0 1.00

7 20.0 0.812

8 22.0 0.671

9 24.0 0.564

1 1 2 3 4 5

g

r

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Distance from Centre of Venus (x 106 _m)

Gravitational Field Str

ength (N/kg)

Gravitational Field Strength Versus Distance from Centre of Venus

analysis

2. a. The distance value doubled.

b. The value of the gravitational field strength was reduced by a factor of 0.25 or 1 4.

3. and 4. In each case, the distance value doubled and the value of the gravitational field strength was very nearly reduced by a factor of 0.25 or 1

4.

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5. Allowing for rounding errors, the pattern in the data is that whenever the distance doubles, the value of the gravitational field is reduced by a factor of 0.25 or 1

4.

6. The value for distance is in the denominator of the equation for gravitational field strength. This means that when distance increases, gravitational field strength decreases. However, the presence of the exponent means that doubling the distance doesn’t make the gravitational field strength 1

2 as much—instead it is 12 2

( )

as much. Since 1

2

2 ₁

2 12 14

( )

=

( )( )

= , the value of gravitational field strength is reduced by 1

4 when distance doubles.

Practice, page 333

11. If the exponent was forgotten and the value for distance was not squared, the denominator of the fraction would have too small a value. This means that the value for gravitational field strength would be much too large.

Practice, page 334

12. Location II

r m g = ¥ = ¥ =

2 00 10

5 98 10

7 24 . . ? m kg g Gm r = =

(

¥

)

(

¥

)

¥

(

)

= -2 11 24 7 2

6 67 10 5 98 10

2 00 10

. .

.

N m /kg kg

m 0.997

2 2

i

N/kg

The gravitational field strength of Earth at location II is 0.997 N/kg.

Location III r m g = ¥ = ¥ =

1 00 10

5 98 10

8 24 . . ? m kg g Gm r = =

(

¥

)

(

¥

)

¥

(

)

= -2 11 24 8 2

6 67 10 5 98 10

1 00 10

. .

.

N m /kg kg

m 0.039

2 2

i

99 N/kg

The gravitational field strength of Earth at location III is 0.0399 N/kg.

Location IV r m g = ¥ = ¥ =

2 00 10

5 98 10

8 24 . . ? m kg g Gm r = =

(

¥

)

(

¥

)

¥

(

)

= -2 11 24 8 2

6 67 10 5 98 10

2 00 10

. .

.

N m /kg kg

m 0.009

2 2

i

997 N/kg

The gravitational field strength of Earth at location IV is 0.009 97 N/kg.

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Location V r m g = ¥ = ¥ =

3 457 10

5 98 10

8 24 . . ? m kg g Gm r = =

(

¥

)

(

¥

)

¥

(

)

= -2 11 24 8 2

6 67 10 5 98 10

3 457 10

. .

.

N m /kg kg

m 0.00

2 2

i

33 34 N/kg

The gravitational field strength of Earth at location V is 0.003 34 N/kg.

13. Location V

r m g = ¥ = ¥ =

3 83 10

7 35 10

7 22 . . ? m kg g Gm r = =

(

¥

)

(

¥

)

¥

(

)

= -2 11 22 7 2

6 67 10 7 35 10

3 83 10

. .

.

N m /kg kg

m 0.003

2 2

i

334 N/kg

The gravitational field strength of the Moon at location V is 0.003 34 N/kg.

Location VI r m g = ¥ = ¥ =

1 84 10

7 35 10

6 22 . . ? m kg g Gm r = =

(

¥

)

(

¥

)

¥

(

)

= -2 11 22 6 2

6 67 10 7 35 10

1 84 10

. .

.

N m /kg kg

m 1.45 2 2 i N N/kg

The gravitational field strength of the Moon at location VI is 1.45 N/kg.

14. a. to c. Earth

Moon

Location V

g



Earth =0 003 34. N/kg g 

Moon=0 003 34. N/kg

d. The gravitational field strength of the Moon is 0.003 34 N/kg, directed toward the Moon. The

gravitational field strength of Earth is 0.003 34 N/kg, directed toward Earth. The strengths of these two gravitational fields are the same, but they act in opposite directions.

e. If a space vehicle comes to rest and turns off its engines at location V, both the Moon and Earth would exert the same gravitational force on it because the strength of the gravitational field from each object is the same. However, because the gravitational fields act in opposite directions, the forces would also act in opposite directions and would cancel out.

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15. a. If the distance from Earth doubles, the value of the denominator in the gravitational field strength equation is increased by a factor of 4. This is due to the fact that the value of r is doubled and then squared, so the overall effect is r2_{is 4 times larger. Since the denominator is 4 times larger, the}

gravitational field strength is only 1

4 of its previous value.

b. If the distance from Earth increases by a factor of 10, the value of the denominator in the gravitational field strength equation is increased by a factor of 100. This is due to the fact that the value of r is made 10 times larger and then squared, so the overall effect is r2_{is 100 times larger. Since the denominator is}

100 times larger, the gravitational field strength is only 1

100 of its previous value.

Practice, page 338

16. a. q r

E

= + =

=

0 0200

10 0 .

.

?

C

m

midpoint 



i

E kq r

=

(

¥

)

(

)

(

)

= ¥

2

9

2

6

8 99 10 0 0200

1 80 10

. .

.

N m /C C 10.0 m

N/C

2 2

The strength of the electric field at the midpoint due to the sphere on the left is 1.80 ¥ 106_N/C.

b. The direction of the electric field at the midpoint due to the sphere on the left is to the right because this is the way that a positive test charge would be forced.

c. Since the values for source charge and distance are the same, the electric field strength will have the same value for the sphere on the right as for the sphere on the left: 7.2 ¥ 106_{N/C. However, the direction}

of the electric field is to the left, since this is the way that a positive test charge would be forced by the source charge on the right.

d. The electric field of the source charge on the left is 1.80 ¥ 106_{N/C, right. The electric field of the source}

charge on the right is 1.80 ¥ 106_{N/C, left. Since these two vectors are equal but opposite, the electric}

fields cancel.

Practice, page 339

17. a. The diagram showing the electric fields around the balloons should look similar to the one given.

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b. Calculate the electric field strength due to one balloon at the midpoint.

r

q

E

= ¥

= = -= - ¥

=

-22 1

0 22

5 0 5 0 10 9

cm m 100 cm m

nC C .

. .

?



i

E kq r

=

(

¥

)

(

¥

)

(

)

=

-2

9 9

2

8 99 10 5 0 10 0 22

929

. .

.

N m /C C

m N/C

2 2

The strength of the electric field at the midpoint due to one balloon is 929 N/C.

Determine the direction of the electric field vectors.

• For the balloon on the left, the electric field due to this source charge will point to the left, since this is the way a positive test body would be forced.

• For the balloon on the right, the electric field due to this source charge will point to the right, since this is the way a positive test body would be forced.

Combine the results from the calculation and analysis to state the final answer.

midpoint

929 N/C 929 N/C

Since the electric field of one balloon is equal in magnitude but opposite in direction to the electric field of the other balloon, the electric field vectors cancel. The result is the net electric field is zero.

Investigation: Using a Coil to Deflect an Electron Beam, pages 340 and 341

This investigation provides a hands-on way to establish two key concepts:

• Moving charges in the form of an electric current produce magnetic field lines. If the current is moving through the loops of a coil, the overall effect is that the magnetic field surrounding the coil is identical to the field produced by a bar magnet.

• When moving charges move through magnetic fields, they can experience a deflecting force. Note that a more detailed description of this force in terms of equations and hand rules is beyond the scope of the Science 30 Program of Studies.

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These concepts play a central role in the next lesson, when students build and analyze motors and generators. This is why this activity is best done as a student-directed investigation rather than a teacher-led demonstration.

The main piece of equipment is a small solenoid (coil) built by the students. The enamelled magnet wire can be purchased on a spool from a local shop that rebuilds alternators and motors. The cost of the wire will depend upon the current world price of copper. The wire is wrapped around a small cardboard cylinder that can be obtained from an empty roll of toilet tissue. The student-built coils will be used in several other investigations throughout the unit, so it is worthwhile to save these devices at the end of the activity.

Part A of this investigation is quite straightforward, and most students will recognize the pattern of magnetic field lines as being the same as the pattern produced by a bar magnet. Part B of this investigation is a little more challenging because the effects students observe occur on such a small scale. Part B is something that you should definitely experience yourself prior to completing the lab with students. The effects can only be observed with a static pattern of different-coloured vertical bars on the screen because students have to notice the slight shift to the left (or to the right) of the boundary between the two colours. Some teachers have noted that this is easier to observe with the test pattern of coloured vertical bars that is broadcast when some channels are “off the air.” You may want to record an hour of the test pattern and then play the tape through a television while the students are completing the investigation.

Note that since the observed shift in colours is due to the deflection of the electron beam within the picture tube of a cathode ray tube (CRT), Part B cannot be done using a monitor that utilizes LCD or plasma technology, since these devices do not utilize electron beams.

Part a: The Magnetic Field Lines around a Current-Carrying Coil

analysis

1. The magnetic field lines seem to form loops that emerge from one end of the coil, curve around, and then enter the other end of the coil. This pattern is shown on the diagram to the right.

This same pattern was observed when a compass was placed at various positions around the outside of a bar magnet.

Even though the power supply is only four AA cells in a battery pack, the coil will generate enough heat that it could become uncomfortable to hold if students maintain the connection to the battery pack for more than a few seconds. It is important to make sure that all students are aware of the recommended safety procedures outlined in the Caution box for the investigation.

Note that the particular end of the coil that the compass needles point to will depend upon the connections to the battery pack and the way the wire is wrapped around the coil.

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