2. Magnetic Field

3. 2 Magnetic Levitation These express trains in Japan are capable of speeds ranging from 225 ~ 480 km/h

4. 3 Magnetic Resonance Imaging A “slice” of human brain

5. 4 Nature of Magnets 1.A magnet can be split into two or more magnets and each of them has N and S poles which cannot be isolated 2. This tells the nature of a magnet: All properties of a magnet come from electric current loops

6. 5 Properties of Magnetic Field Magnetic field is a special type of matter Magnetic field contains energy Interaction between magnetic field and electric current (electric field) Magnetic field strength and direction

7. 6 Magnetic Field Lines Magnetic field lines are used to describe magnetic field Magnetic field lines show both direction and strength of magnetic field

8. 7 Typical Magnetic Field (1)

9. 8 Typical Magnetic Field (2)

10. 9 Similarity of Two Magnetic Fields

11. 10 The Earth’s Magnetic Poles

12. 11

13. 12 Second Right-Hand Rule NS

14. 13 Applications of Electromagnet

15. 14 Applications of Electromagnet

16. 15 How to Calibrate the Sensor Turn FINE control to mid-rotation position Press RUN/20K button, allow a few seconds or the unit to stabilize Zero display using OFFSET knob unless display shows under 0.05 or so Select 2K range and zero display using COARSE control Select 200 range and zero display using FINE control

17. 16 How to Use the Sensor Choose larger range of measurement if no reading Rotate the probe slightly to get peak reading Press STOP to turn off the unit

18. 17 Increase Strength of Electromagnet 1.Use iron (steel) core 2.Increase current (voltage) 3.Increase wraps of solenoid

19. 18 Microscopic Picture of Magnets

20. 19 Magnetic Force

21. 20 Measure of Magnetic Field Magnetic induction, B, is the identity to describe a magnetic field B is a vector so it has magnitude and direction Unit: Tesla or Gauss 1 Tesla = 10 4 Gauss

22. 21 Third Right-hand Rule

23. 22 F = BIL F is in Newton, B is in Tesla, I is in Ampere, and L is in meter

24. 23 Nature of Magnetic Force F is the resultant force that magnetic field exerts on all moving charges F = BIL=> I = q/t=> t = L/v => I =q/t = qv/L => F = B(qv/L)L = Bqv

25. 24 Steps to Compute Magnetic Force Measure distance the pipe moved Compute θ and F in reference of the FBD Measure B and L Compute F by F = BIL Compare the two Fs What makes the two Fs different θ T F 0.2 N

26. 25 Paper cone attached to coil Sound signal converted to varying electric current

27. 26 Galvanometer

28. 27 Electric Motor

29. 28 Key Procedures to Build a Motor Make wire about 1 m long Remove coating on only ONE and SAME side of the straight parts of the wire Do not set the current greater than 1 amp

30. 29 Electromagnetic Induction

31. 30 Electromotive Force (EMF) EMF should be called electromotive potential Unit of EMF is Volt EMF = BLV(maximum value)

32. 31 Electric Guitar

33. 32 Tape Recorder

34. 33 Electric Generator

35. 34

36. 35 Difference of Generator and Motor

37. 36 Effective Current & Effective Voltage Similarly,

38. 37 Lenz’s Law The direction of the induced current is such that the magnetic field resulting from the induced current oppose the change in the field that cause the induced current. Result opposes cause

39. 38 Lenz’s Law Illustration

40. 39 Transformer

41. 40 How Can EMF Be Induced? If and only if there is a changing magnetic field around the conductor or circuit. Movement of either the magnetic field or the conductor (circuit) is not necessary.

42. 41 Ignition System

43. 42

44. 43 Example Problem A straight wire 0.20 m moves perpendicularly through a magnetic field of magnetic induction 0.008 T at a speed of 7.0 m/s. What EMF is induced in the wire? Solution: EMF = BLv = (0.008 T)(0.2 m)(7 m/s) = 0.11 V