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1 Electricity & Magnetism Unit I - Charge Behavior and Interactions –Charge produces and responds to an electric field Unit II - Electric Potential –An electric field can store energy Unit III - Circuits –The electric field can cause bulk charge flow in conducting materials Unit IV - Magnetism –Charge flow produces and responds to a new field

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2 What’s the same? Many of the labs and activities are very familiar –Sticky tape, Coulomb’s Law –Mapping electric potential –Ohm’s Law, resistance in series and parallel –Mapping magnetic field Many of the exercises are familiar

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3 So, what’s different? Develop models to account for observed phenomena Use these models throughout the entire set of materials –Diagrammatic representations, causal mechanisms stressed over QPS using plug-n- chug approach

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4 I- Charge and Field Emphasis on atomic model of matter –charge is a fundamental property of matter (like mass) –charge carriers are microscopic constituents of matter –behavior of charged objects results from uneven charge distribution

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5 I- Charge and Field Compare and contrast electrical and gravitational forces –force arises from fundamental property of objects (mass vs charge) –inverse square relationships between point particles –differences in magnitude and direction

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6 I - Charge & Field Emphasis placed on origin and nature of the field –arises from uneven distribution of charge –strength is the force per unit “something” –mediates the force between charges –stores energy due to interactions

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7 II - Potential & Energy Continue analogy with gravitational field –Relate electric equipotentials to contour lines on a topographic map

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8 II - Potential & Energy Continue analogy with gravitational field –Relate electric equipotentials to contour lines on a topographic map –Potential is property of position in field –Changes in potential energy depend on field strength, change in position and a property of the object

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9 II - Potential & Energy Formulas are developed in context of energy storage and transfer

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10 II - Potential & Energy Formulas are developed in context of energy storage and transfer Rearrangement yields essential relationships

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11 III - Circuits Emphasis on causal mechanisms rather than application of Ohm’s and Kirchoff’s Laws –field responsible for bulk flow of charge in conductors –∆V accounted for by differences in charge density Study of circuits no longer disconnected from field and potential developed earlier

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12 III - Circuits Influences –Sherwood and Chabay article “A Unified Treatment of Electrostatics and Circuits” surface charge distribution responsible for field –CASTLE curriculum unequal initial flow rates can cause compression or depletion of charge

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13 III - Circuits Paradigm labs examine what’s happening in the wires as well as in resistors –use voltage probe to measure ∆V in wire during transient –make charge distribution maps to account for ∆V infer existence of field –must also exist in wires if charge is to flow –field strength dependent on charge distributions

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14 III - Circuits Sketch the charge distribution and field in the intervals midway through the discharge of the capacitor through the long bulb. Sketch a diagram that you feel describes the charge distribution, wire size and field midway through the discharge of the capacitor through the round bulb. In what ways are the diagrams similar? How are they different?

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15 IV - Magnetism Moving charge produces and responds to a magnetic field 1st lab - mapping field produced by charge moving in a wire –RH curl rule –field strength increases with current and decreases with distance

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16 IV - Magnetism Compare/contrast with electric field –E-field - static charge, lines originate from (+) and terminate on (-) –B-field - moving charge, lines form closed loops Magnetic domains in “permanent magnets” result of electron spin

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17 IV - Magnetism Demo to show how force acts on wire carrying current. Mr BIl’s swing is deflected out from magnetic field when current runs through the wire RH palm rule Sets up lab with current balance

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18 IV - Magnetism Small motor project application of Lorentz force on loop Loop rotates to align B fields Sets stage for introduction of flux and induction

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19 Materials are a work-in-progress Magnetism least well-developed of the E&M units Instructional notes in all units need work to more coherently develop story line Feedback from Modeling teachers should help

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Electrostatics, Circuits, and Magnetism 4/29/2008

Electrostatics, Circuits, and Magnetism 4/29/2008

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