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Workshop material for week 13 • Material covered in lectures in week • Introduction • Review of sections • Reflection and formula sheets • Homework • Quiz Introduction • Welcome • News: Exam 3: Chs. 27, 28 and 29, Nov. 25 • List sections covered in week and homework Sections 29.1 Induction experiments 29.2 Faraday’s law 29.3 Lenz law 29.4 Motional EMF 29.5 Induced electric fields Homework 11 th Ed. Sect. 29.2: 29.2, 5, 9 Sect. 29.3: 29.16, 17 Sect 29.4: 29.20, 24, 25 Sect. 29.5: 29.31 12th Ed. or 2, 4, 9 or 15, 17 or 20, 25, 26 or 30 29.1 Induction experiments & 29.2 Faraday’s law • Use demo to show induction of a current by means of a changing flux • Ask students to identify the variables involved (strength of B, area of loop, velocity, angle between loop and B field) • Ask students to identify cases when the magnetic flux increases and decreases • Ask students to justify Faraday’s law d B A d BA cos d B dt dt dt • Show that when there is a constant flux there is no current induced • If possible show that if angle between B and area is 90o the flux is zero • Explain that the negative sign refers to the direction of the induced current and will be det5ermined by Lenz’s law in the next section • Pose problem 29.5 and solve it on board with help from the students (15 min) • Let students work problem 29.9 in groups (10 min) 29.3 Lenz’s law • Explain that Lenz’s law is used to determine the direction of the current induced according to the following steps: • Determine if the flux is increasing or decreasing • Establish that the induced current will produced an induced B field • Choose the direction of the induced B field so that it DOES NOT help the change of flux • Pose the following examples and invent a few more • Pose problem 29.15 and solve it on board with help from the students (15 min) • Let students work problem 29.17 in groups (10 min) 29.4 Motional EMF • Draw the slidewire generator and ask the class to explain how it works • Apply a velocity to moving bar to produce a current in loop • Ask student to go from the velocity to the current step by step (v moves bar, increases fluc, induces an EMF, creates an E field inside wire, which generates a current) • Ask for its variables (velocity, area, B) and establish dependen ce of EMF with variables • Derive expression for EMF as follows: d BA d A B dt dt dt d Lx dx B BL BLv dt dt d B • Pose problem 29.25 and solve it on board with help from the students (15 min) • Let students work problem 29.26 in groups (15 min) 29.5 Induced electric fields • Draw the slidewire generator • Ask the class if an electric field is created inside the wire • Ask student for ideas on how to obtain such E • Derive E as follows: EMF: Vab vBL Taking E as uniform, then Vab EL E vB • In general (even when E is not uniform): This can be used to obtain E at any point d B E dl dt • Work the example of the following two slides in detail with the help of the class (15 min) • Let students work problem 29.30 in groups (15 min) d B E dl dt d B 1 d B E dl Edl E 2 r E dt 2r dt The direction is determined using the right-hand rule d B dB dI A 0n A dt dt dt 410 7 Wb Am 500 turns m 100 A 4 10 m s 4 2 25 106 V 1 d B 1 dI E 0n A 2r dt 2r dt 1 2510 6 V 2 10 4 V/m 2 0.02 m Reflection: Important concepts seen Ask students to reflect about what are the most important concepts of the following sections and write on board (5 min) • 29.1 Induction experiments • 29.2 Faraday’s law • 29.3 Lenz law • 29.4 Motional EMF • 29.5 Induced electric fields Formula/Concept sheet for exam Ask students to come up with important concepts to include in the formula sheet for exam 1 (5 min) Homework •Let students ask questions about the homework assigned •Write statement of problem on board •Give chance to students to answer •Summarize answers, work on board, do not finish problem •Give students time to re-work homework •Repeat last three steps until there are no more questions •Take a maximum of (10 min) per problem Quiz • Assign a quiz based on a medium-hard numerical problem like those assigned in the homework • Give them a maximum of 15 min Dismissal • Return quizzes