3 Lesson What Is Electricity? Student Book pages 10 11 In this lesson: Students explore the nature of electricity and experiment with static electricity. Specific Outcomes evaluate various methods for producing electrical charges (T1) communicate their observations, experiences, and thinking in a variety of ways (P3) manipulate and control a number of variables in an experiment (P14) work cooperatively with others (A1) show scientific interest and curiosity (A2) show increasing confidence as scientific problem solvers (A9) Assessment Consider how well students can explain where the buildup of excess electrons must be to cause the attractive forces. (Excess electrons on an object move or pull things, showing the observer which attractive force is present negatively and positively charged materials attract one another, and materials of the same charge repel one another.) (T1, P1, P5) After the Exploration, ask students to write descriptions and make drawings to show what happened to the balloons after they were rubbed with wool. Observe whether students use the correct terms and know when they have charged things or produced an attractive force. (T1, P3) Getting Organized Time Required: Activate 10-15 min; Explore 15-20 min; Apply 20-25 min Advance Preparation: Gather materials. Lesson Vocabulary static electricity: a form of electricity resulting from the accumulations of imbalanced charges on the surface of objects charge: a quality of electricity that can be either positive or negative; similar charges repel each other and opposite charges attract each other positive: in a charge, produced by the lack of electrons negative: in a charge, produced by an excess of electrons electrons: negatively charged particles atoms: the smallest particle of an element that has the properties of the element electric discharge: the rapid movement of electrons away from a charged object Lightning strikes in the atmosphere, which might be occurring hundreds of kilometres away, cause most of the static you hear on your AM radio. 20
Content Background Electricity is the work of subatomic particles called electrons. Everything around us, including our bodies, contains these particles, so everything can be thought of as being partly electric. Electricity can be seen in nature as lightning, as aurorae, and in electric eels. In static electricity, an electric charge collects on the surface of an object due to the loss or gain of electrons. The buildup of the charge is the result of the redistribution of charges in the object. In current electricity, the electrons move through objects or substances. We can easily produce static electricity by picking up particles from the surface of one object and depositing them somewhere else as when you rub particles off a carpet with your shoes and deposit them on a receptive doorknob with your hands. Thanks largely to the pioneering work of seventeenth-century French scientist Charles du Fay, we know that there are two charges, and that similar charges repel, and opposite ones attract. Benjamin Franklin invented the idea of an electric charge, labelling an excess of electric charge as positive (+) and a deficiency as negative ( ). Franklin s experiments led him to believe that lightning is a giant spark of static electricity, and thunder is a huge crackle of static charge. In 1752, in Philadelphia, Franklin proved his hypothesis he succeeded in capturing some electricity to use in his experiments by flying a kite before a lightning storm. A wire attached to the top of his kite attracted a negative charge from a storm cloud. Electric current travelled down the wet kite string toward a metal key and ultimately to a Lewden jar designed to store electric energy. Franklin was lucky to survive his experiment others who have tried the experiment have been killed by the lightning. Lightening is a spectacular example of electric discharge. Lightning is the electrostatic spark that results from the rapid movement of charged particles within a thundercloud or between the cloud and the ground, the air, or another cloud. There are numerous types of lightning. The most common type is intracloud lightning, in which internal charges form a spark. When the flow of charges is between the cloud and Earth, the result is cloud-to-ground lightning (what most people see) or ground-to-cloud lightning, depending on the direction in which the charges flow. 21
Activate Explore Have You Seen Electricity? Ask students: Have you ever seen any evidence of electricity? (Students may report having seen blue sparks of static electricity, an electric current escaping from a damaged appliance, and lightning bolts. Some students may have seen demonstrations of high-voltage electric currents in a science museum.) Invite students to describe how these different electric currents are similar in shape, sound, and colour, but have different intensities. Introducing Static Electricity Have students read the introductory paragraph. Encourage them to recall any instances when they received shocks of static electricity. What was similar about these situations? What do you think caused the shock? Write their responses on the board or chart paper to return to later when writing the characteristics of static electricity. Some students may think that electricity is limited to batteries and wall sockets. You may wish to do a brief demonstration with a fluorescent lighting tube and some plastic wrap. Darken the room and rub a section of the tube vigorously with the plastic wrap. It will glow where it was rubbed. Ask students to predict why the tube began to glow and what this demonstration has in common with electric shocks that come from rubbing stocking feet on a carpet. Preconceptions Students may not understand how a shock from a doorknob happens. This lesson will help them understand how static charges build up. Preparing for the Exploration Suggested Grouping: pairs Approximate Time: 15-20 min Materials per Group: balloons, wool, plastic wrap, silk, paper, felt, goggles, pens/pencils, Science Journals (Student Book page 10) Make static electricity. 1. Make sure students are wearing goggles when they start this experiment. 2. Ask what they think makes the balloons stick to the walls and each other. Explain to students that an electric charge on the balloon, called a static charge, makes the balloons stick to the wall and to each other. 3. When the balloons are rubbed with wool, they will repel one another. 4. Discuss the idea of fair test with the students. Remind them that they should only change one variable in an experiment at a time. Ask them to choose several different materials, write out their steps to compare the materials, and show it to you before they start. Students can record their results in a chart. Troubleshooting For best results, conduct this experiment on a cool, dry day, preferably in the winter. Exploration Results The balloons rubbed with silk, plastic wrap, felt, and paper also produce static electricity. 22
Apply Interpret your results. (Student Book page 10) The balloons stuck to the wall for a few minutes. Students observe that rubbing the balloons more vigorously will increase the length of time they cling to the wall. The balloons repelled one another. The longer students rub the balloons, the more they repel one another. The balloons attract one another and stick to each other for a short time. Static charges can either attract or repel each other. Communicate your results. Ask students to share their thoughts about how their balloons reacted on a chart and compare their charts. The differences in results come about because of different variables in the experiment: for example, how much they rubbed the balloons and for how long. Exploration Connection (Student Book page 11) Charged on static electricity Ask students to read the text on page 11 of the Student Book and answer the questions at the end. Students will realize that because the balloon and the wall were attracted to each other, they had different charges. The green balloon moves forward and makes contact with the orange balloon. Some of its negative charge then moves to the orange balloon. At that point, the two negatively charged balloons would repel each other. Students will find that when they rub their hands over a static balloon, electrons are being removed and the balloon loses its electric charge. Make an Electroscope You or a group of students could make an electroscope for students to use in testing whether materials are charged (see Reproducible 3A: Make an Electroscope). Students can first touch the foil the foil ball with items that have not been charged and observe the results (nothing happens). Then students can charge items such as pens or glass rods, by rubbing them on silk or wool. Have students explain answers when items they have charged are placed near the end of the foil ball: - Where did the excess electron charges go? - What happens to the strips of foil? - Why do the foil strips move apart? (An object is given a positive charge by rubbing on silk or wool. When the positively-charged object is held near the foil ball, negative charges are drawn up the wire to the ball, and only positive charges are left on the folded foil strip. Since like charges repel one another, the foil pieces move apart.) 23
Apply Ask: What happens if you touch the foil ball? Have students rub stocking feet on a rug to create a static charge on their bodies and then touch the foil ball again. Ask students to explain (orally or in a labelled diagram) the path the electrons took from the rug to their stocking feet, along their bodies, to their hands, and onto the ball. Characteristics of Static Electricity With the students, make a list of the characteristics of static electricity. (It is caused by positive and negative charges on an object.these charges attract or repel other objects with negative and positive charges.) Keep this list to compare with the characteristics of current electricity in Lesson 4. Struggling/ESL Students Ask students to look up the definitions for static and static electricity in a dictionary. Knowing that static means not moving may help them understand that static charges are at rest on the surfaces of objects. Encourage them to look for other words with stat as their root (e.g., stationary, statue). Your dry clothes stick together because static charges can build up on the fabric when the garments rub together as you move. Global Perspectives The discoveries that led to the use of electricity as an energy source started with the study of static charges. German scientist Otto von Guericke laid the groundwork for modern electric experimentation by devising a machine to produce static electricity. His machine, built in 1660, was essentially a sulphur ball turned by a hand crank. When von Guericke rubbed his hand on the revolving ball, he produced static charges. After careful experimentation, he noticed that static charges can repel as well as attract. He originated the concept of transmitting electricity when he sent a static charge down a few feet of thread to attract fluff. His electrostatic generator also produced noisy sparks of light, inspiring further studies about the nature of electricity. 24
Extending Learning Electric Comb Have students complete Reproducible 3B: Charged Comb. Discuss their results, including which part they find is rubbing on or off electrons for an attractive force, and whether changing the material changes the type of attractive force. Lightning Ask students to investigate lightning. When and how does it occur? How can you tell how far away it is? What safety rules should everyone follow when there is lightning? Brainstorm a list of questions about lightning and students pick one to find the answer to share with others. Preventing Static Charges Bring to class two fabric softener sheets ( dryer cloths marketed to reduce static electricity in a clothes dryer). One of the sheets should be used, the other new. Students can examine the cloths and predict how a cloth might work to reduce static electricity. (The dryer s heat releases a chemical from the sheet that forms a coating on clothes so electrons are not so easily rubbed off the clothes.) Have students investigate techniques for preventing static charges (for example, grounding, and raising humidity to reduce static charges). They can present their findings in the form of labelled diagrams. Charged Water Students can learn more about static charge by observing how a static charge deflects a stream of water. Materials: balloon, sink with running water 1. Blow up a balloon and tie it closed. 2. Unplug the sink and run a very thin stream of water from the tap. 3. Rub the balloon on your clothing. Without getting the balloon wet, hold it near the stream of water. What happens to the water? (Students will observe that the stream of water moves toward the electrically charged balloon.this means that the side of the stream nearest the balloon carries a charge opposite to the balloon.) 25
3A Name Date Make an Electroscope 1. If the wire is covered in insulation, remove the covering from about 5 cm at each end. Push the wire through the covering for the jar. (If you re using a cork or rubber stopper, make a hole through the centre of the stopper using the nail. If you re using a cardboard disc, make a small hole in the middle of the disc using the scissors and tape the wire in place.) 2. Check that about 10 cm of the wire is showing through the top, and about 20 cm through the bottom of the covering. Bend the lower end of the wire at right angles to make a flat hook. You need: small glass jar, completely dry inside cork or rubber stopper or cardboard disc to fit top of glass jar copper wire (about 20 cm) thinfoilstripfrom gumwrapper (about 3 cm x.5 cm) aluminum foil optional: nail or tape and scissors foil ball 3. Fold the foil strip in half and hang it over the wire hook. (Check that there is no insulation between the foil and the wire.) 4. Cover the bottle tightly with the stopper or disc. Use tape if necessary to hold it in place. Make sure the foil stays on the wire. 5. Crumple the foil into a ball, and press it around the top of the wire. gumwrapper foil 6. Test charges by holding an object next to the foil ball. Observe what happens to the foil strip. 26 Copyright 2005 Scholastic Canada Ltd.This page may be reproduced for classroom use by the purchasing school.
Name Date 3B Charged Comb How can a comb be used to demonstrate static electricity? Design an experiment in which you rub a comb on a piece of wool and then test to determine if there is an attraction to a variety of materials (such as bits of paper, feathers, hair, and so on). Use this page to help you plan your experiment and record your results. 1. What is the question you would like to answer? 2. What is your hypothesis? (You can record several hypotheses, and then choose the one you think is best.) 3. Which materials will you test? 4. Which variables will you control? 5. Which variable will you change? 6. Record your observations. 7. What do you conclude based on your observations? 8. Was your hypothesis supported? Give reasons why or why not. Copyright 2005 Scholastic Canada Ltd.This page may be reproduced for classroom use by the purchasing school. 27