1. HW7 due on Friday Turn in HW6 Stand by to receive back HW5 EXAM 2 coming up on Monday !!!!! March 30 th

2. Magnetic field due to a long (straight) wire: Let’s review:

3. current on ( I up ! ).

4. Right hand rule (#1)

5. ( I up/out ! ). DIRECTION-OK MAGNITUDE???

6. Experiment shows: For a long straight wire

7. Example: Suppose a cable is carrying 100 A current. What’s the B-field 1 cm from the cable? How about 10 cm?

8. Example: The cables are each carrying 25 A out the of page. What’s at point Q? 13.0 cm Q

9. Example: The cables are carrying 25 A out the of page. What’s at point P? Superposition! Next … 13.0 cm P

10. P Example: The cables are each carrying 25 A out the of page. What’s at point Q?

11. P Now: Vector Superposition! Next …

12. Example: The cables are each carrying 25 A out the of page. What’s at point Q?

13. Forces between current-carrying conductors

18. Opposite Currents Repel!

21. Parallel Currents attract! (same magnitude as other case!)

22. Example: What force per unit length do two cables 1 cm apart produce on each other? (They’re carrying 50 A each.) How about at 10 cm?

23. What about currents perpendicular to each other? …

25. Fun example: Force/m?

26. Fun example: How much current do you need in the third wire so the net forces are zero?

27. Current Loop: up/out down/in Solenoids

28. Current LoopS: up/out down/in

30. Solenoid: up/out down/in

31. WRENCH DEMO

32. Example: What’s the B-field inside a coil with 50 turns/cm, running a current of 2 A?