1. hitt Two long straight wires pierce the plane of the paper at vertices of an equilateral triangle as shown. They each carry 3A in the same direction. The magnetic field at the third vertex (P) has the magnitude and direction (North is up): (1) 20 μT, west (2) 17 μT, east (3) 15 μT, north (4) 26 μT, south (5) none of these 4 cm P

2. Long, straight, parallel wires carry equal currents into or out of page. Rank according to the magnitude of the force on the central wire, largest to smallest. 1. d, c, a, b 2. a, b, c, d3. b, c, d, a4. c, a, b, d 5. b, d, c, a

3. A horizontal power line carries a current of 5000 A from south to north. Earth's magnetic eld (60 μT) is directed towards north and inclined down-ward 50 degrees to the horizontal. Find the magnitude and direction of the magnetic force on 100 m of the line due to the Earth's field. (1)23 N, west(2) 23 N, east(3) 30N, west (4) 30N, east (5) none of these 50 B N I

4. Chapter 30 Induction and Inductance In this chapter we will study the following topics: -Faraday’s law of induction -Lenz’s rule -Electric field induced by a changing magnetic field -Inductance and mutual inductance - RL circuits -Energy stored in a magnetic field (30 – 1)

5. (30 – 6)

6. NS magnet motion (30 – 7)

7. N S magnet motion (30 – 8)

8. S N magnet motion (30 – 9)

9. S N magnet motion (30 –10)

10. (30 –11)

11. (30 –12)

12. (30 –13)

13. (30 –14)

14. (30 –15)

15. (30 –16)

16. loop 1 loop 2 (30 –17)

18. (30 –19)

19. (30 –20)

20. (30 –21)

21. N2N2 N1N1 (30 –22)

22. N2N2 N1N1 (30 –23)

23. N2N2 N1N1 (30 –24)

24. Electrons are going around a circle in a counterclockwise direction as shown. At the center of the circle they produce a magnetic field that is: A. into the page B. out of the page C. to the left D. to the right E. zero e

25. Long parallel wires carry equal currents into or out of the page. Rank according to the magnitude of the net magnetic field at the center of the square. 1. C,D, (A,B)2. A, B, (C,D)3. B, A, C, D 4. D, (A, B), C

26. Partial Loops (cont.) Note on problems when you have to evaluate a B field at a point from several partial loops –Only loop parts contribute, proportional to angle (previous slide) –Straight sections aimed at point contribute exactly nothing –Be careful about signs, e.g.in (b) fields partially cancel, whereas in (a) and (c) they add

27. (30 – 2)

28. loop 1 loop 2 (30 – 3)

29. (30 – 4)

30. loop (30 – 5)