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Physics HS/Science Unit: 08 Lesson: 01 Suggested Duration: 10 days Electrostatic Forces, Fields, Energy, and Interaction with Matter Lesson Synopsis: This unit develops an understanding of electrostatics by the use of demonstrations, simulations, and modeling. The general theme is that the current model of matter consisting of electrically neutral atoms composed of charged particles is integral to the understanding of electrical forces. The lesson begins with traditional activities of charging objects by friction and comparing electrostatic forces to magnetostatic forces. The traditional experiments are explained in terms of the model of an atom, and the “attract and repel force rules” are explored and expanded. Devices to create, store, and measure charge are utilized in experiments. The formal theory of Coulomb’s law is introduced, and problems are assigned utilizing that theory. Elements of the historical development of electrostatics and planetary model of the atom are researched, and students have an assignment describing contributions of historically important scientists. Additional concepts of electric fields, potential difference, and properties of conductors and insulators are developed through experiment, demonstration, and discussion. TEKS: P.5 P.5A P.5C P.5E P.6 P.6B The student knows the nature of forces in the physical world. The student is expected to: Research and describe the historical development of the concepts of gravitational, electromagnetic, weak nuclear and strong nuclear forces. Supporting Standard Describe and calculate how the magnitude of the electrical force between two objects depends on their charges and the distance between their centers. Supporting Standard Characterize materials as conductors or insulators based on their electrical properties. Supporting Standard Science concepts. The student knows that changes occur within a physical system and applies the laws of conservation of energy and momentum. The student is expected to: Investigate examples of kinetic and potential energy and their transformations. Readiness Standard Scientific Process TEKS: P.1 P.1A P.2 P.2F P.2J Demonstrate safe practices during field and laboratory investigations. The student uses a systematic approach to answer scientific laboratory and field investigative questions. The student is expected to: Demonstrate the use of course apparatus, equipment, techniques, and procedures, including multimeters (current, voltage, resistance), triple beam balances, batteries, clamps, dynamics demonstration equipment, collision apparatus, data acquisition probes, discharge tubes with power supply (H, He, Ne, Ar), hand-held visual spectroscopes, hot plates, slotted and hooked lab masses, bar magnets, horseshoe magnets, plane mirrors, convex lenses, pendulum support, power supply, ring clamps, ring stands, stopwatches, trajectory apparatus, tuning forks, carbon paper, graph paper, magnetic compasses, polarized film, prisms, protractors, resistors, friction blocks, mini lamps (bulbs) and sockets, electrostatics kits, 90-degree rod clamps, metric rulers, spring scales, knife blade switches, Celsius thermometers, meter sticks, scientific calculators, graphing technology, computers, cathode ray tubes with horseshoe magnets, ballistic carts or equivalent, resonance tubes, spools of nylon thread or string, containers of iron filings, rolls of white craft paper, copper wire, Periodic Table, electromagnetic spectrum charts, slinky springs, wave motion ropes, and laser pointers. Organize and evaluate data and make inferences from data, including the use of tables, charts, and graphs. P.2K Communicate valid conclusions supported by the data through various methods such as lab reports, labeled drawings, graphic organizers, journals, summaries, oral reports, and technology-based reports. P.3 The student uses critical thinking and scientific reasoning, and problem solving to make informed decisions within and outside the classroom. The student is expected to: P.3A P.3D P.3E ©2012, TESCCC The student conducts investigations, for at least 40% of instructional time, using safe, environmentally appropriate, and ethical practices. These investigations must involve actively obtaining and analyzing data with physical equipment, but may also involve experimentation in a simulated environment as well as field observations that extend beyond the classroom. The student is expected to: In all fields of science, analyze, evaluate, and critique scientific explanations by using empirical evidence, logical reasoning, and experimental and observational testing, including examining all sides of scientific evidence of those scientific explanations, so as to encourage critical thinking by the student. Explain the impacts of the scientific contributions of a variety of historical and contemporary scientists on scientific thought and society. Research and describe the connections between physics and future careers. 01/10/13 page 1 of 16 Physics HS/Science Unit: 08 Lesson: 01 Performance Indicator(s): • Complete a lab report describing, explaining, and analyzing electrostatics demonstrations and phenomena in terms of the atomic structure of matter, principles of conservation of charge, electric forces, electric fields, and electrostatic energy. (P.2K; P.5C, P.5E; P.6B) 1E; 4J • Research and describe in a summary the contributions of Franklin, Millikan, and Coulomb in the development of electrostatics and atomic structure theory. (P.3D; P.5A) 4I; 5F Key Understandings and Guiding Questions: • • • • Electrical properties of matter include insulation and conduction. — What makes an object a good insulator or a good conductor? The development of electrostatic theory and the atomic model of matter are closely related. — How does our atomic model of matter help us understand electrostatic phenomena? — How can we use electrostatic phenomena to confirm our atomic model of matter? The concepts from “mechanics” of forces, fields, and energy also describe the electrical interactions of charges. — What are the similarities between gravitational quantities properties and electrical phenomena? — How will studying mechanics help in the study of electricity? The concept of electrostatics was developed through the contributions of a number of people. — How has the concept of electrostatics changed over time? Vocabulary of Instruction: • • • • • • • • • charge polarization Coulomb’s law insulator potential energy shielding electroscope induction cathode ray • • • • • • • • • electrostatics potential difference Coulomb vector magnitude electrophorus electromagnetic force capacitor electric force • • • • • electric field volt conductor law of conservation of energy Van de Graaf generator Materials: Refer to Notes for Teacher section for materials. Attachments: • • • • • • • • • • • • • • Teacher Resource: Rotating Fork Demonstration Handout: Charge Magnet Attract (1 per student) Handout: Summary Report on Magnetic Pole and Electric Charge Interactions (1 per student ) Teacher Resource: Summary Report on Magnetic Pole and Electric Charge Interactions KEY Handout: Using an Electroscope (1 per student) Teacher Resource: Using an Electroscope KEY Handout: Charging by Induction (1 per student) Handout: Build an Electrophorus (1 per student) Handout: Electric Field Hockey (1 per student) Handout: Coulomb’s Law Applications (1 per student) Teacher Resource: Coulomb’s Law Applications KEY Handout: Electrical Scientists – Discover the Atom Research Paper (1 per student) Teacher Resource: Video: Crook’s Tube Demonstration Handout: Model of the Atom (1 per student) ©2012, TESCCC 01/10/13 page 2 of 16 Physics HS/Science Unit: 08 Lesson: 01 • • • • • • • • • • • Handout: Electrostatic Applications (1 per student) Teacher Resource: Electrostatic Applications KEY Handout: Electric Fields and Equipotential Lines (1 per group) Handout: Equipotential Surfaces Computer Lab Activity (1 per group) Teacher Resource: Equipotential Surfaces Computer Lab Activity KEY Handout: Electric Fields in a Parallel Plate Capacitor (1 per student) Handout: Electric Fields in a Parallel Plate Capacitor Lab Report KEY Teacher Resource: Van de Graaff Generator Demonstrations Handout: Properties of Conductors (1 per student) Teacher Resource: Video: Sharp Points Teacher Resource: Video: Faraday Cages Resources and References: • Suggested Websites: • Website Videos: • http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html (Use the index in the right column to find the demonstrations.) • http://amasci.com/emotor/vdg.html • Van de Graaff Generator Demonstrations: http://www.amasci.com/emotor/vdgdemo.html#thr • Rutherford Experiment: http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf • Millikan Oil Drop Experiment: http://highered.mcgrawhill.com/sites/0072512644/student_view0/chapter2/animations_center.html • Simulations: • PhET group at the University of Colorado at Boulder: http://phet.colorado.edu/new/index.php. • Balloon and Static Electricity: http://phet.colorado.edu/new/simulations/sims.php? sim=Balloons_and_Static_Electricity • Electrostatic Hockey Program: http://phet.colorado.edu/new/simulations/sims.php? sim=Electric_Field_Hockey • http://micro.magnet.fsu.edu/electromag/java/rutherford/ • Charges and Fields: http://phet.colorado.edu/new/simulations/sims.php?sim=Charges_and_Fields Advance Preparation: 1. Make sure software for simulations is installed and compatible with your computers and networks. 2. Prepare attachments as necessary. Background Information: Since it is not possible to see charges, electric fields, current, etc., most students have conceptual difficulty at times with physics. It is helpful to develop a mental model about what is going on and then to test that model often. The physics may not seem “real” to the student at first. It should be clear that much of the evidence for the atomic model of matter comes from the study of electrostatics and that this atomic model is useful in understanding electricity and magnetism concepts. There are many misconceptions about electricity and electromagnetism; thus, it is important that these misconceptions are addressed as they arise in the lesson. All magnets and therefore, magnetic fields, result from charges in motion (electrical currents) followed by the fact that magnetic fields exert forces on moving charges. Magnetic fields are produced by moving charges and also influence the motion of charges. If the magnetic fields are varying, as with alternating current, then the changing current produces changing magnetic fields. These magnetic fields, in turn, produce (induce) changing electric fields as in a transformer. Finally, light and other electromagnetic fields are a combination of changing electric and magnetic fields interacting with (two faces of the same phenomena) each other. GETTING READY FOR INSTRUCTION SUPPLEMENTAL PLANNING DOCUMENT Instructors are encouraged to supplement and substitute resources, materials, and activities to differentiate instruction to address the needs of learners. The Exemplar Lessons are one approach to teaching and reaching the Performance Indicators and Specificity in the Instructional Focus ©2012, TESCCC 01/10/13 page 3 of 16 Physics HS/Science Unit: 08 Lesson: 01 Document for this unit. Instructors are encouraged to create original lessons using the Content Creator in the Tools Tab located at the top of the page. All originally authored lessons can be saved in the “My CSCOPE” Tab within the “My Content” area. INSTRUCTIONAL PROCEDURES Instructional Procedures Notes for Teacher ENGAGE – Introduce the Topic with a Demonstration and Questions NOTE: 1 Day = 50 minutes Suggested Day 1 1. Using the Teacher Resource: Rotating Fork Demonstration, perform the demonstration. This activity will take approximately 10 minutes. Ask: • What is happening – what force is causing the fork to rotate? Do not volunteer the answer to the students unless they actually know. Possible student responses should include magnetic and electrical forces. 2. Project the following questions on the board, and ask students to record them in their science notebooks. Inform students they will be learning the answers to the questions during the next two units. • What are the rules for electric charges and magnetic poles attracting and repelling? • Do magnets attract or repel charges? What is the rule? • What color are charges? • What do they weigh? • What reaches out and causes the force which causes the fork to rotate? Can you see it? 3. Remind students of the importance of forming models to help us understand phenomena, illustrate concepts, and also guide our predictions in new experiments. Ask: • What is our model of matter? This question is just to confirm that the students begin thinking about atoms, electrons, protons etc. Materials: • metal fork • putty • glass test tube • ball point pen • 3" x 3" block of wood with a hole drilled into the center to hold the pen • electrophorus plate Attachments: • Teacher Resource: Rotating Fork Demonstration Instructional Notes: The purpose of the lesson is to review electrostatic and magnetostatic phenomena in an engaging manner, possibly dispel some misconceptions, and create a common set of experiences that can be used in class discussions. The report, discussed at the end of the period, on magnetic pole and electric charge interactions provides a convenient summary of the rules for electrostatic charges and magnets at rest. Determine whether you can do electrostatics activities today by rubbing a balloon with wool and sticking it to the wall. (This also sets the stage for the class.) If you cannot stick a balloon to the wall, it is probably too humid to do a good job with electrostatics activities. Practice the rotating fork demonstration before you do it for the class. Science Notebooks: Students record focus questions in their notebooks to answer throughout lessons. EXPLORE – Magnets and Charges Suggested Day 1 (continued) 1. Divide students into groups of 2–3. This activity will take approximately 15 minutes. ©2012, TESCCC 01/10/13 page 4 of 16 Physics HS/Science Unit: 08 Lesson: 01 Instructional Procedures Notes for Teacher 2. Distribute to each student a copy of the Handout: Charge Magnet Attract. 3. Instruct students to test materials with magnets and the charged rod to see if they are attracted, repelled, or have no interaction. 4. Instruct students to fill out the chart on the handout as they test each material. Materials: (per group) • magnets – ring or bar magnets • electrostatic kit including objects to test with magnets (paper, tin foil, penny, salt, pepper, paper clip, ….) • balloon • cellophane tape • wool or fur • plastic rods to create static charges Attachments: • Handout: Charge Magnet Attract (1 per student) Misconception: • Students may think that a charged body has only one type of charge. EXPLAIN Suggested Days 1 (continued) and 2 1. Facilitate a post-lab discussion in which students present the results of their testing. 2. Ask different groups which items were attracted to magnets, which to charges, and which to both. This activity will take approximately 25 minutes. Notes: • The magnets attract only steel objects – not all metal objects. • Magnets and charges act differently. They are different quantities. 3. If necessary for clarification, demonstrate that the paper clip is attracted to the charged rod once the paper clip is made easier to move by hanging it by a thread. 4. Review with students: If two objects are attracted, the less massive one is the one that will move most easily; thus, charged scotch tape is attracted to everything. (Charge the cellophane tape by “peeling” it off of a balloon.) Show that the charged tape is attracted to the paper clip. A 5–6 inch strip of tape works well. 5. Instruct students to re-test the non-attracting things with charged cellophane tape strips. They should use the non-sticky side. 6. Instruct students to correct their charts with the new information and discuss their findings with their groups. 7. Distribute to each student a copy of the Handout: Summary Report on Magnetic Pole and Electric Charge Interactions. • As a class, or in groups, discuss the questions and/or perform tests which allow students to answer the questions on the handout. • Challenge them to find anything that is not attracted to the charged tape. ©2012, TESCCC 01/10/13 Materials: (teacher only) • paper clip • thread (per group) • magnets – ring or bar magnets • electrostatic kit including objects to test with magnets (paper, tin foil, penny, salt, pepper, paper clip, ….) • cellophane tape • balloons • wool or fur • plastic rods to create static charges Attachments: • Handout: Summary Report on Magnetic Pole and Electric Charge Interactions (1 per student) • Teacher Resource: Summary Report on Magnetic Pole and Electric Charge Interactions KEY Instructional Notes: Students will find that several things are not attracted to charges, such as the paper clip. Indicate to students that this result is probably due to mass and the object is too heavy to move with the relatively small charges in this page 5 of 16 Physics HS/Science Unit: 08 Lesson: 01 Instructional Procedures Notes for Teacher experiment. Hang a paper clip from a thread, and show that the paper clip is attracted to the charged rod. The purpose of using the charged rod first instead of beginning with the scotch tape tester is to remind them of previous labs (earlier in school grades) and how they might have been confused earlier. They may have been told the correct answer, but their experience may not have justified that answer. Science Notebooks: If students record observations in their student notebooks, only one copy will be needed per group. ENGAGE – Quick Demonstrations Suggested Day 2 (continued) 1. This activity will take approximately 15 minutes. Review yesterday’s activities with students. Rub a balloon with wool or fur, and stick it to the wall. Do the same thing with a balloon rubbed with plastic wrap. 2. If running water is available, a small, smooth stream of water will be attracted to a charged rod or balloon. Ask: • What charge is the water (+ or -)? (Neutral) • Since we cannot see charges but know the rules for attraction and repulsion of charges, how do we explain that charged objects attract neutral objects? (Neutral objects are charged both positively and negatively, and the polarization aspect explains their attraction to both positive and negative charges.) • How can we tell the sign of a charged object? (By bringing it near another object with a known charge) • What is the sign of the charge on the balloons on the wall? (The wool rubbed balloon will have a negative charge.) • Are they charged the same or different? How could we find out? (The balloon rubbed with plastic wrap acts the very same as the balloon rubbed with wool but is positively charged and can be determined by bringing it near another positively charged object.) • What does the rubbing do? (Charging by friction; some things lose electrons and some gain electrons) 3. Relate the demonstration to the discussion questions. 4. Principles also illustrated include the following, and these should be addressed quickly. • Insulators (The charges do not move, but remain fixed.) • Conservation of charge • Forces are stronger when the charges are closer (set up for Coulombs law later). 5. Our model of matter (neutral atoms with positive and negative charges) allows a reasonable explanation for all of the observations. ©2012, TESCCC 01/10/13 Materials: (teacher only) • balloon • wool • fur • plastic wrap (per group) • wool • plastic wrap • cotton • electroscope • fur • plastic rod • foam cup • glass • vinyl strip • acetate strip • wood rod • balloon • fork • Simulation: Balloon and Static Electricity: http://phet.colorado.edu/new/simulat ions/sims.php? sim=Balloons_and_Static_Electricity Instructional Notes: Today’s activities emphasize how charged objects attract neutral objects through polarization of the neutral page 6 of 16 Physics HS/Science Unit: 08 Lesson: 01 Instructional Procedures Notes for Teacher molecules. This leads to a discussion of the use of electroscopes, how they work, and how they can be used to tell the charge sign of objects. The Balloons and Static Electricity simulation from the Internet should be displayed to the class. It should be tested prior to class. In the simulation, the wool rubbed balloon will have a negative charge, and the polarization of the wall is evident. The term polarization should be introduced in this context. The real balloon rubbed with plastic wrap acts the very same as the real balloon rubbed with wool, but is positively charged. This is an opportunity to discuss the importance of models to explain what we cannot see. It is difficult to tell the charge sign on the balloons since simple attraction is not sufficient. The balloons will rotate to make the attraction if placed near to each other. Repulsion is definitely a charge-charge interaction, but attraction may be between a neutral object and a charged object. Neutral molecules become polarized through the attraction and repulsion of their positive and negative charges with the opposite charges closer and thus attract stronger than the like charges repel. EXPLORE – Detecting Charges and Signs Suggested Day 3 1. Distribute the Handout: Using the Electroscope and materials. Instruct the students to perform the tests indicated in the activity. Allow about 35 minutes for the activity. 2. If needed, demonstrate how the electroscope works by performing one of the tests as an example. It is important that students understand how to tell the charge sign on objects by using the electroscope. 3. Facilitate a discussion of the lab report, and answer any questions. 4. Relate the results of this activity to the questions asked at the beginning of class. ©2012, TESCCC 01/10/13 Materials: (per group) • wool • plastic wrap • cotton • electroscope • fur • plastic rod • foam cup • glass • vinyl strip • acetate strip • wood rod • balloon page 7 of 16 Physics HS/Science Unit: 08 Lesson: 01 Instructional Procedures Notes for Teacher • fork Attachments: • Handout: Using the Electroscope • Teacher Resource: Using the Electroscope KEY EXPORE/EXPLAIN – Making an Electrophorus Suggested Days 3 (continued) and 4 1. Review the differences between these terms: conductor, insulator, nonconductor, and dielectric. Point out that the last three terms are used interchangeably. Remind students of the properties learned so far. Ask: • If you wanted to store charge for later use and get it out fast, to light a bulb or use it some other way, would you store it on an insulator or conductor? (From a conductor, so the charge can move) 2. Inform students they will learn how to charge objects in a new way, called induction, and will look at an early device used for storing charges. 3. Demonstrate the electrophorus, charging and discharging the plate with a fluorescent bulb. 4. Emphasize that first, the base must be charged by friction and that this charge is not used up. The fact that the bulb lights several times in the demonstration illustrates this concept. Ask: • How much voltage is needed to light the bulb? (Over 100 volts) • Where is the energy coming from? (The energy comes from rubbing the wool on the plate creating a negative charge.) 5. Discuss, again, how the electrophorus is charged. Note the strip of cassette tape will react as the plate is charged. 6. Distribute the Handouts: Charging by Induction and Build an Electrophorus. 7. Instruct students to complete the Handout: Charging by Induction to illustrate how to charge an electroscope by induction and verify the sign of the charge is opposite of the inducing charge. 8. Instruct student groups to construct and demonstrate an electrophorus. Groups should be able to show how the neon bulb can be flashed with the electrophorus. 9. Instruct students to write a brief summary report in their student notebooks, explaining how to charge by induction. They can use the electrophorus or the electroscope as a specific example. 10. When students complete the investigation, collect the summary report that explains how to charge an object by induction. Materials: (per group) • electroscopes • materials to construct an electrophorus: • foam plate • aluminum foil plate • foam cup • cellophane tape • cassette tape strip • student neon bulb • small fluorescent bulb if available Attachments: • Handout: Charging by Induction (1 per student) • Handout: Build an Electrophorus (1 per student) Safety Notes: While not dangerous to most students, it is wise to see if any students may have medical conditions that would preclude them from mild shocks. Warn students that electronic devices, such as watches and cell phones, can be damaged by high voltage shocks. Electrostatic activities have a high voltage. Check for Understanding: The summary report will assist students in preparation for the Performance Indicators at the end of the lesson. Instructional Notes: ©2012, TESCCC 01/10/13 page 8 of 16 Physics HS/Science Unit: 08 Lesson: 01 Instructional Procedures Notes for Teacher The topics today include conductors, insulators, dielectrics, charging by induction, using an electrophorus, and grounding. Science Notebooks: Students complete their summaries in their notebooks. You can also make group copies of the handouts and instruct students to do the initial work in their notebooks as well. EXPLORE – Gravity Forces vs. Electrical Forces 1. 2. 3. Suggested Day 4 (continued) Facilitate a discussion of Newton's law of gravitation, and then, introduce to students an exploration of electrostatic forces through an electrical game simulation. This can be done by asking students questions. Ask: • What is a gravitational field? (A force field that exists around any object that has mass) • What is the source of this field? (Mass of the object) • We know there are forces between charges, how are they similar and different from gravity forces? (These forces attract and repel differently. Both gravitational and electrical forces decrease as the distance between the force increases.) Say/Ask: • We recognize mass as the source of gravity forces and charges as the source of electrostatic forces. • How do the forces between charges and masses change with distance and with the "size" of the "sources"? (As distance increases, the force decreases) • Are the attraction forces as strong as the repelling forces for charges? (Yes, they depend on distance.) • Do the electrical forces cause motion like gravitational forces? (Yes, if the force is strong enough.) Distribute the Handout: Electric Field Hockey. Instruct students to read and then discuss any questions they may have. Students are asked to master at least the first two levels of the simulation and answer questions about how forces interact. 4. Divide students into small groups to conduct the investigation, and remind them they will work in small groups, but be prepared to turn in the lab report at the end of the period. 5. Facilitate a class discussion in which students share their results and discuss the following Guided Questions: • What are the similarities between gravitational quantities properties and electrical phenomena? (Gravitational and electrical quantities change inversely as distance changes.) • How will studying mechanics help in the study of electricity? (The energy due to the position or movement of an object can be related to electrical phenomena.) ©2012, TESCCC 01/10/13 Materials: (per group) • computer • Simulation: electrostatic hockey program: http://phet.colorado.edu/new/simulat ions/sims.php? sim=Electric_Field_Hockey Attachments: • Handout: Electric Field Hockey (1 per student) Instructional Notes: Students should be familiar with the way that gravity forces act at a distance, the universal gravitational force equation (Newton's gravity equation), and the concept of a gravity field. Use this background to introduce Coulombs law and the electric field. The concepts and equations are similar. Foci for the discussion: • There are similarities and differences between gravitational and electrical forces. • These forces attract and repel differently. • Both gravitational and electrical forces decrease as the distance between the force increases. Misconception: • Students may think an electric field and force is the same thing. page 9 of 16 Physics HS/Science Unit: 08 Lesson: 01 Instructional Procedures 6. Notes for Teacher When students complete the investigation, collect the Handout: Electric Field Hockey. EXPLAIN – Theory Discussion 1. 2. Following a discussion of the lab activities, a formal discussion of Coulomb's law and the Electric field should be held. A discussion of this theory should present the points below: • Coulombs law is Felectric = k(q1 q2 /d2 ), where Felectric is the interaction force between two charges, q1 and q2, where k=9x109 Nm2/C2. Coulomb's law works ONLY for two charges and gives the value of the force on both. The attraction force equation for opposite charges and repulsion force equation for like charges are the same. • The unit of charge is Coulomb, and the name of the equation is Coulomb's law. • If there are several charges, the total force on the target charge is the vector sum of the Coulomb forces on that charge. In the lab, the puck was the target charge. • The total electric field at the location of the target charge due to all of the other charges is the total force on that charge divided by its charge. E = F/q - E has units of N/C and is vector in the direction of the total force on a positive charge at that location. • Repeating: E is the electric field at a location due to all other charges, which are not at that location and is the force per charge at that location in space. • If the electric field at some location is known, then the force on a charge at that location is F = qE. • In electricity and magnetism, the emphasis tends to be more on the electric field (force per charge) than the force. Similarly, the emphasis is with potential difference which is potential energy per charge rather than on potential energy. • The electric field points away from positive charges and toward negative charges. Show with diagrams. Instructional Notes: A possible short homework assignment is given to solidify some of the language and concepts. Schedule the assignment to be due the next day. STAAR Notes: The Physics STAAR Reference Materials include the formula for Coulombs law as noted. Provide students with the Handout: Coulomb’s Law Applications. EXPLAIN/EXPLORE – History and Models of the Atom 1. Suggested Days 4 (continued) and 5 Attachments: • Handout: Coulomb’s Law Applications (1 per student) • Teacher Resource: Coulomb’s Law Applications KEY Knowing the evidence for the model of matter and how that evidence was obtained, provides students with a deeper understanding of the model. Ask: Encourage student answers but indicate that the history of this model is the focus for today. • How did we develop our model of an atom? (As technology improved, the experimentation with the atom provided more information about the structure of the atom) • What holds the atom together? (Electrostatic force) • How do we know the nucleus size, the relative mass of nucleus and the electron? (Evidence from Rutherford’s scattering experiment) • Do all electrons have the same charge? (Yes, negative) 2. Some significant persons in the story of our planetary model of an atom are Franklin, Millikan, Coulomb, Rutherford, and JJ Thompson. 3. Students will be researching the contributions of these scientists in relation to the understanding of electrostatics and the model of an atom. ©2012, TESCCC 01/10/13 Suggested Days 6 and 7 Materials: • Simulation: http://micro.magnet.fsu.edu/electro mag/java/rutherford/ • Simulation: Rutherford experiment at the URL: http://www.mhhe.com/physsci/chemi stry/essentialchemistry/flash/ruther1 4.swf • Millikan Oil Drop experiment at the URL: http://highered.mcgrawhill.com/sites/0072512644/student_v iew0/chapter2/animations_center.ht ml page 10 of 16 Physics HS/Science Unit: 08 Lesson: 01 Instructional Procedures Notes for Teacher The Handout: Electrical Scientists – Discover the Atom Research Paper serves a guide for the assignment. 4. Note: This research can begin today with the teacher sharing the video, URL, and animations with the class, and the remainder of the time can be spent researching the contributions of the scientists. Students should take notes on the handout to be used for completing the research paper. 5. Project the Video: Crook’s Tube Demonstration, indicating the charge is negative and is very light, as evidenced by the ability to alter its path easily. The electrons are ripped from the electrode and accelerated through a vacuum where they strike a phosphorescent screen. This gives the appearance of a beam of electrons, however, it should be emphasized that we see the flash on the screen, not the electrons. This is very similar to CRT television sets. The Crook's tube demonstration video and simulation is intended to show that all matter has electrons. These particles come from the negative electrode (negatively charged) and are easily deflected. We have not studied the magnetic field—moving charge interaction, but it provides the easiest way to move the beam. 6. Show the following URL - applet of the Rutherford scattering experiment. Explain what is happening to the class, or let them view the site below or both. For the Florida State URL, the slit should be opened up to allow the alpha particles to encounter gold foil nuclei allowing large angle scattering. The Rutherford scattering experiment disproved Thompson's plum pudding model of an atom that contends that the positive charge (pudding) contained electrons (raisins). The very heavy alpha particles would not have been deflected by the light electrons and would have been slowed down by the pudding. This was not what happened. The backscattered alpha particles proved the gold nucleus was very heavy, positively charged, and very small. http://micro.magnet.fsu.edu/electromag/java/rutherford/ 7. Instruct students to view an animation with narration and explanation of the Rutherford experiment at the URL: http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14 .swf 8. Instruct students to view and take notes for the research paper, from a simulation lab of the famous Millikan Oil Drop experiment at the URL: http://highered.mcgrawhill.com/sites/0072512644/student_view0/chapter2/animations_center.htm l 9. Review the Handout: Model of an Atom, which can serve as a summary sheet. 10. Facilitate a class discussion in which students reflect on the relevant changes. Ask: • How does our atomic model of matter help us understand electrostatic phenomena? (The presence of charges in the atom and how they interact relates to electrostatic charges.) • How can we use electrostatic phenomena to confirm our atomic model of matter? (Electrostatic forces within the atom explain how the atom is held together.) • How has the concept of electrostatics changed over time? (This ©2012, TESCCC 01/10/13 Attachments: • Handout: Electrical Scientists – Discover the Atom Research Paper (1 per student) • Handout: Model of the Atom (1 per student) • Teacher Resource: Video: Crook’s Tube Demonstration Instructional Notes: Students are aware of the model of an atom containing a nucleus with electrons outside, but may not understand the evidence for this model and how this interacts with electrostatics. This is a good time to develop the history and evidence for the atomic model. We will look at some of the people and experiments that led to this model. Some of the story (energy levels and spectra) will need to wait until we get into modern physics. Students are shown demonstrations, assigned history writings, and are reminded of activities in which they have participated. The Handout: Model of the Atom serves as a reminder to the students for later study. It also helps students in their research paper. page 11 of 16 Physics HS/Science Unit: 08 Lesson: 01 Instructional Procedures Notes for Teacher concept has proven that matter has two kinds of charge, all matter has electrons, electrostatic forces hold atoms together, and charges are distributed in the atom.) 11. Remind students to continue work on their historical research papers, which will be due on Day 10 of this unit. EXPLORE/EXPLAIN – Potential Energy and Potential Difference Equations and Problems 1. Equations for potential energy, potential difference, and the related theory are the focus for the day’s lesson. 2. In relation to a positive charge in the electric field produced by a negative charge, Ask: • Where does that positive charge have more potential energy? (Farther away) • Where would it have zero potential energy? (Zero PE place is normally at r = ∞) 3. Demonstrate the voltmeter and measure the potential difference of different sources. Make the point that the potential energy and potential energy per charge (voltage) require a zero reference point. Hence, the real name for voltage is potential difference (the difference in potential energy per unit charge) between two locations. The unit for potential difference is volt. 4. For charges, the zero PE place is normally at r = ∞. Thus, the potential difference - the voltage for a negative charge is a negative number which has a larger absolute value as you get closer to the negative charge. We use the term voltage, or potential, when we are casual - in the same way that we use the term mileage when we mean distance between two locations. 5. The following set of quantitative concepts should be explained and used while modeling calculations to aid in the basic understanding of the material: • Coulombs Law – force between two point charges • Electric field from a point charge at a distance from the charge (charge is source of E) • Vector addition of E from more than one charge (simple geometry) • Force on charge in that field is F = qE • All charges are multiples of electronic charge. q = N e • The potential energy between two point charges (the energy is in the interaction) stress this is a scalar. U=kq1q2/r • The number of interactions for 2 charges is 1, for 3 charges it is 3, for 4 charges it would be 6, and so on. These are scalar interactions but may be positive or negative • The potential difference (commonly called voltage) at a given location for a point charge. (potential energy per charge) • For several charges, the total potential difference at a location is the algebraic sum of contributions from charges. • For charged objects (not point charges, specific equations for those objects must be used to calculate E, V, U, etc.) • For a parallel plate capacitor, the electric field inside the plates is constant. ©2012, TESCCC 01/10/13 Suggested Day 8 Materials: (teacher only) • voltmeter • batteries of various sizes Attachments: • Handout: Electrostatic Applications (1 per student) • Handout: Electrostatic Applications KEY Instructional Notes: It is possible to spend a lot of time working electrostatics problems. They can be difficult and tricky or straight forward. Since not all resources (books, Internet, worksheets, etc.) use the same symbols for all of the quantities, you should be careful in sending the students to the web for tutorial help. It is important when using formulas to use the Physics STAAR Reference Materials as a resource for students to use when performing calculations. STAAR Notes: The Physics STAAR Reference Materials include the formula for electric potential energy-distance as noted. page 12 of 16 Physics HS/Science Unit: 08 Lesson: 01 Instructional Procedures 6. Notes for Teacher Distribute the Handout: Electrostatic Applications, and instruct students to complete the calculations. EXPLAIN/ELABORATE – Electric Fields and Equipotential Surfaces Suggested Day 9 Materials: (per group) • Simulation from PHET – Charges and Fields: http://phet.colorado.edu/new/simulat ions/sims.php? sim=Charges_and_Fields Attachments: • Handout: Electric Fields and Equipotential Lines (1 per group) • Handout: Equipotential Surfaces Computer Lab Activity (1 per group) • Teacher Resource: Equipotential Surfaces Computer Lab Activity KEY Instructional Notes: Students have done some electrostatics exploration in general, and they have looked at the model of matter and the history validating parts of the model. They know Coulombs law, have made a few simple calculations, and have been introduced to the electric field. Today, they explore the electric field in more detail. 1. Today, students explore the relationship between charges, electric fields, and electric potential difference using a simulation. The analogy between equipotential gravitational surfaces (a table top for example) and equipotential electrical surfaces can be a powerful learning tool. 2. Use the Handout: Electric Fields and Equipotential Lines to introduce and/or review the terminology of equipotential lines or surfaces. Perform a quick demonstration of the PHET program to assist the students in making quick progress in the lab. Distribute the Handout: Equipotential Surfaces Computer Lab Activity. Assist the students in performing the investigation. 3. 4. 5. Facilitate a class discussion in which students share their results. Clarify any misunderstandings. 6. When students complete the investigation, collect the Handout: Equipotential Surfaces Computer Lab Activity. ©2012, TESCCC 01/10/13 The normal convention is that electric fields end on negative charges and get less strong (absolute number) as you get farther from the charge, similar to the gravitational field from a planet or a Sun. This lesson is intended to strengthen the concept of electric field and to connect it to the electric potential difference. The analogy with the equivalent concepts in the study of gravity should still be useful. First, establish some conventions and common background terminology. The analogy is that the gravity field points down. Surfaces with the same potential energy are horizontal. Thus, the equipotential surfaces are page 13 of 16 Physics HS/Science Unit: 08 Lesson: 01 Instructional Procedures Notes for Teacher perpendicular to the gravity field. This is the same with electrical quantities. ELABORATE – Electric Fields in a Parallel Plate Capacitor Conductors Shield Electric Fields from Outside 1. The concepts explored on this day are related to the previous activity and the simulation is used. 2. Ask one or more of the following questions: • If you wanted to perform an experiment on the hazards or benefits of electric fields on humans, how would you produce a region with constant electric fields? This question may not develop good responses, but can get to the point that E results from charges and that point charge fields vary with distance. The answer is to place the experiment within a parallel plate capacitor. • Have you ever had trouble getting a portable radio (or cell phone) to work inside a metal structure? Conductors shield electric fields from the outside. • Why do you want to be riding in an old Chevy sedan instead of a Corvette when struck by lightning? The Chevy is made of metal, and the Corvette is plastic; thus, the metal protects you from the lightning. It is not that “the wheels ground” you from the charge as some would say. In fact, you want to drain the charge away so a path to ground is good. 3. Remind students that capacitors are used to store electrical energy and have other uses in electrical circuits. The parallel plate capacitor is an important learning example in physics and illustrates a number of concepts. 4. Distribute a copy of the Handout: Electric Fields in a Parallel Plate Capacitor, and instruct students to complete the investigation. This investigation utilizes the “Charges and Fields” simulation. 5. Instruct students to complete the handout using the simulation. 6. Briefly discuss student findings, and answer any questions related to electric fields and capacitors. 7. When students complete the investigation, collect the Handout: Electric Fields in a Parallel Plate Capacitor. ELABORATE – Van de Graaff Generator Materials: (per group) • Simulation from PHET: “Charges and Fields” http://phet.colorado.edu/new/simulat ions/sims.php? sim=Charges_and_Fields Attachments: • Handout: Electric Fields in a Parallel Plate Capacitor (1 per student) • Handout: Electric Fields in a Parallel Plate Capacitor Lab Report KEY Instructional Notes: The Charges and Fields simulation software is excellent in explaining the connection between equipotential surfaces and the direction of electric fields. The point of the simulation is that the electric fields for the charges on the inside of the conductors (capacitor plates) are blocked by the conducting plates. Thus, the fields are not basically present outside the interior of the capacitor. This is not true for the two lines of charge in the simulation held in place on an insulating base. This is an important property of conductors for static charges - electric fields are zero within (inside) the conducting material. Suggested Day 10 1. Begin the class with a few demonstrations from the Teacher Resource: Van de Graaff Demonstrations. 2. Ask: • What is the voltage of the Van de Graaff generator? 100 V, 1,000 V, 10,000 V, or 100,000 V? Voltages of over 100,000 are not uncommon. To estimate, a 1 cm spark for dry air requires 30,000 volts for flat surfaces. • Is this voltage dangerous? Why or why not? It is not dangerous because it is current that is fatal, not voltage. The normal static shock, which can be on the order of 10–40 kv, is not fatal because it is very low current. • How does the generator work? ©2012, TESCCC Suggested Day 9 (continued) 01/10/13 Materials: • Van de Graaff generator • fluorescent bulb • neon bulb • thread • cotton • aluminum foil plate • soap bubbles • foil covered cardboard page 14 of 16 Physics HS/Science Unit: 08 Lesson: 01 Instructional Procedures Notes for Teacher If possible, disassemble to the point where students can view the essential parts. 3. If it is not possible to disassemble the generator, display a diagram from a hyperphysics site and point out the essential parts: • metallic dome • moving belt • sharp pointed wires on both ends (linking the belt to …) 4. Distribute the Handout: Properties of Conductors, which is the basis for the lecture-discussion-demonstration. 5. Read each statement, and either discuss, illustrate, or demonstrate to allow students to understand and believe what is occurring. Students will take notes on the handout. Explain how a Van de Graaff generator works, using the principles on the sheet. 6. 7. Perform additional demonstrations with the generator, and discuss how the rules of electrostatics explain the demonstrations. • • • • • • • • • aluminum foil pieces tissue paper strips rice crispy cereal piece of wire paperclip Internet with class display to show Internet demonstrations Website video: http://hyperphysics.phyastr.gsu.edu/hbase/hframe.html (Use index on the right column to find demonstrations.) Website video: http://amasci.com/emotor/vdg.html Website: Van de Graaff Generator Demonstrations: http://www.amasci.com/emotor/vdg demo.html#thr Attachments: • Teacher Resource: Van de Graff Generator Demonstrations • Handout: Properties of Conductors (1 per student) • Teacher Resource: Video: Sharp Point • Teacher Resource: Video: Faraday Cages Safety Notes: While not dangerous to most students, check for students who may have medical conditions that would preclude them from mild shocks. Instructional Notes: Today, the focus will be on introducing the concept that conductors shield electric fields from the outside. The Van de Graaff generator is used to engage this topic as well as the Handouts: Properties of Conductors and Discussion of Hollow Conducting Sphere. This portion of the lesson is intended to make sure that students know the properties of conductors, have a visual experience to convince them that they are true, and reinforce what is meant by the statements. The instructor basically reads the ©2012, TESCCC 01/10/13 page 15 of 16 Physics HS/Science Unit: 08 Lesson: 01 Instructional Procedures Notes for Teacher properties one by one and asks if this is clear and/or provides a demonstration or example (shown on the statement) to clarify the concept. At the end of the handout, these concepts are used to explain how a Van de Graaff generator works. There are a number of ways to explain that the charge goes to the outside of a conductor. One way is to indicate that a conductor is all at the same potential, everything inside is at that potential, and thus, there is no tendency for current flow. EVALUATION – Performance Indicators Performance Indicators • Complete a lab report describing, explaining, and analyzing electrostatics demonstrations and phenomena in terms of the atomic structure of matter, principles of conservation of charge, electric forces, electric fields, and electrostatic energy. (P.2K; P.5C, P.5E; P.6B) 1E; 4J • Research and describe in a summary the contributions of Franklin, Millikan, and Coulomb in the development of electrostatics and atomic structure theory. (P.3D; P.5A) 4I; 5F ©2012, TESCCC 01/10/13 Suggested Day 10 (continued) Instructional Notes: The Performance Indicators for this unit have been completed during this unit and should indicate a student’s understanding of the concepts related to electrostatic forces. Students can use the prior lab reports and research paper as a reference for completing a report that describes, explains, and analyzes the demonstrations and phenomena explored in this lesson. page 16 of 16