1. Today4/23  Magnetic Induction Review  HW Questions?  Exam 4/24  Force and motion of charged particles  B-fields due to wires  Force and Torque on current loops  Forces from currents (like 4/16 Wires 2)  Induced current (like 4/17)

2. Magnetic Induction  The current only flows while:  the B-field is changing  the ring is moving  the magnet is moving  It’s all about a “changing” B field!!!  Look at whether the # of field lines are increasing or decreasing

3. Force on Current Loops  Ch 21: Force/Torque arises from a battery operated loop in a static B-field.  Ch 22: Current in loops “induced” by a “changing” external field. The loop then reacts as in Ch 21.  In fact, battery operated loops resist the changing field caused by themselves! Called “Self Induction” see 22.8

4. Faraday’s & Lenz’z Law E = -  tt  is the # of field lines inside loop Lenz’s Law Loop “Voltage”  can change in many ways: changing B-field changing loop area changing loop angle changing B-field angle This is the “equation” you will see on the exam

5. E = -  tt Using  Identify initial field direction  Identify final field direction  Determine direction of the “change”  Use Lenz’s law to determine B-field due to the current induced around the loop  Use RHR #2 to find direction of induced current

6. Energy Considerations  It takes energy to push current around a loop  Therefore, forces arising from induced currents must always serve to retard (or slow down) the object