1. Today4/17  Magnetic Induction, Ch 22  HW: 4/17 “Induced Current” Due Thursday, 4/24  Friday and Monday are holidays!  Exam 4/24  Force and motion of charged particles  B-fields due to wires  Forces from currents (like 4/16 Wires 2)  Induced current (like 4/17)

2. Magnetic Induction We need a model for the jumping ring There is no battery to push current around the ring as was the case in all examples so far. (See 4/10 and 4/11 HW) Major Question: What pushes current around the loop????

3. moving ring Magnetic Induction First clue comes from this example: S N Use RHR #1

4. Magnetic Induction S N moving magnet Same current as when ring moves!

5. Magnetic Induction Same current as when ring moves! What if I make the magnet appear suddenly? S N

6. Careful!!!!  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

7. moving ring Magnetic Induction First clue comes from this example: S N Field lines point left and are increasing

8. Magnetic Induction S N moving magnet Field lines point left and are increasing

9. Magnetic Induction S N Field lines point left and are increasing

10. The Minus sign (again!)  The current in the loop will flow so as to “oppose” the “change” in the # of lines.

11. moving ring Magnetic Induction Change points left- loop fights it right -current as shown. S N Field lines point left and are increasing

12. Magnetic Induction S N moving magnet Field lines point left and are increasing Change points left- loop fights it right -current as shown.

13. Magnetic Induction S N Field lines point left and are increasing Change points left- loop fights it right -current as shown.