Good Luck! Exam 2 Review Phys 222 Supplemental Instruction SUNDAY SESSION AS NORMAL, INFORMAL Q/A

Transcription

1 Good Luck! Exam 2 Review Phys 222 Supplemental Instruction SUNDAY SESSION AS NORMAL, INFORMAL Q/A

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3 The correct solution process is the right answer

4 Do you know all the following?

5 Circuits Current, Voltage, Resistance, Ohm s law Power, Real Batteries, measuring tools (ammeter etc) Analyze circuit diagrams and circuits with multiple voltage sources Combining circuit elements, reducing circuits to equivalent setups

6 Magnetic fields Field lines Impact on moving charges Relation to Electric field Magnetic forces (Lorentz force) On currents and current loops Hall effect Fields Generated by current (Biot-Savart law) Ampere s law Magnetic dipoles, dipole interaction

7 Induction Faraday s law Lenz s law Eddy currents Magnetic materials Paramagnetism, diamagnetism Inductors and energy storage Time varying circuits LR, LC, LRC Phasor Diagrams Resonance Conditions Transformers

8 Here we go! LOTS OF TEST PROBLEMS WITH TIPS SPRINKLED IN

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10 RHR Really all the uses are subsets of just two right hand rules and can be gotten from the two. 1. RHR cross rule. Point fingers in direction of first vector, curl fingers toward second vector and thumb points in the direction of the resultant. 2. RHR curl rule. Point thumb in direction of current and fingers curl in direction of B field.

11 Right Hand Rule(s)! Torque on a magnetic dipole Use standard RHR, cross product Magnetic Force on a moving charge, by a field Use standard RHR, cross product Magnetic Field generated by a current Thumb in direction of current, fingers curl in direction of field. Circulation integrals Curl fingers in direction of integration, thumb points in direction that positive current flows. Induced current (Faraday s law) Thumb in direction opposing change in magnetic flux, fingers curl in direction of the induced current.

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13 Magnetic Field Field produced by a charge, moving at speed v: B = μ 0 qv r 4π r 2 Use RHR to determine direction the magnetic field points (modified curl version) Field produced by many charges, aka current: db = μ 0 Idl r 4π r 2 Once again, dl x r just means to use the modified (curl) RHR This equation is perhaps easier to use as: B = μ 0 IL r 4π r 2

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18 Combining components Capacitors Resistors / Inductors Addition T = X1 + X2 + Inverse Addition 1/T = 1/X1 + 1/X2 + Parallel Inverse Addition 1/T = 1/X1 + 1/X2 + Addition T = X1 + X2 + Series

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20 Field lines! Magnetic field lines are loops, no start or end! Magnetic field lines appear to leave North pole and enter south pole. Line density indicates field strength

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24 Faraday s law Regards changes in FLUX Flux changes are changes in magnetic field strength or area of the loop enclosed. Remember Magnetic flux is the integral of B da Usually BA The induced current always opposes the change in magnetic flux. If flux is decreasing, it will try to increase it, and vice versa Lentz s law Sign s? Always check your signs at the end with reality and Lentz s law. It s easy to get negative signs messed up in Magnetism.

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26 Ampere s Law: B dl = µ*i encl Solve these problems just like Gauss s law problems! Draw a picture. Pick a good Gaussian surface. Symmetry! Write expression of integral (if B A then, BA) Write expression for Gauss s Law involving enclosed magnetic field Set the expressions equal and eliminate variables to solve.

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28 Inductor and Capacitor Behavior Capacitors: Initially: Ideal Wire Long time: Open Switch Inductors: Initially: Open Switch Long time: Ideal Wire

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30 Formulas, Formulas The new material has formulas on page 3 mainly. Don t forget µ o is a constant (on pg 1) Think about dot products and cross products geometrically. Dot products give parallel components Cross products give perpendicular components Make sure to know the formulas vs the definitions.

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32 Hodgepodge OF RELEVANT QUESTIONS

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42 Type Susceptibility Reaction in Field Physical Description Diamagnet < 0 (small) Weakly Repelled (normal nonmagnetic materials) Paramagnet > 0 (small) Weakly attracted Soft Ferro large Strong temporary Attraction Hard Ferro large Strong Permanent Magnetization Weak antialignment of material s dipoles Weak alignment of dipoles Alignment of magnetic domains Example Wood, Water Liquid Oxygen Refrigerator Iron, Neodynium

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