Magnetic Fields and Electromagnetism

1. Magnetic FieldsandElectromagnetism Created for CVCA Physics By Dick Heckathorn 19 April 2K+4

2. 18.1 Natural Magnetism 676 • Investigation • How Do Magnetic Regions • Relate To Each Other? Magnets

3. What is the interaction force? Repulsive Repulsive Attractive

4. Magnetic Fields • What is a magnetic field? • What is the symbol for magnetic field? • What is its usefulness? • How do we see a magnetic field?

5. Investigation • Viewing a magnetic field Magnets – spheres in Plexiglas

6. Magnetic Field Around a Bar Magnet

7. The Magnetic Field Between Unlike Poles

8. The Magnetic Field Between Like Poles

9. Demonstrate • Tie a paper clip to a string. Then move the arrow above the large magnet. • Which way does the field really point? Large Magnet - Arrow

10. Investigate • Place a magnet on a piece of paper. • Move a compass around the magnet keeping the compass on the paper. Bar magnet – compass – piece of paper

11. Investigate 3. Create the following.

12. Investigate 4. Would this be the end result if one mapped the whole area?

13. Magnetic Fields • How do we detect a magnetic field? • (compass) • What is the direction of a magnetic field? • (direction north seeking end • of compass points)

14. A Question Equally huge – Newton’s 3rd Law

15. A problem

16. Demonstration • Which end of a magnet • points north? 2 Bar magnets – magnet holders - support

18. Question • How does the • earths magnetic north pole • compare to the • earth geographic north pole? • Handout: Magnetic Declination 2 Bar magnets – magnet holders - support

20. Magnetic Declination

21. Demonatration • Breaking a magnet Special magnets – compass - overhead

23. Investigation • Magnetizing • a temporary magnet • using a nail • and • DC current. Battery – nail – wire – paper clips

24. 18.2 Electromagnetism 681 • What did Oersted discover? • Moving electric charges produce a magnetic field.

25. Investigation • What exists around a current carrying wire? • How is its direction defined? Power Source – coils of wire - compasses

27. What one would see with a magnetic field viewer.

28. Question • How can one predict the direction of • the magnetic field? • Grab wire with thumb in direction of current, fingers give direction of field.

30. Thumb? • Direction of current. • Fingers? • Direction of magnetic field.

31. Investigation • What exists around a single coil of wire with a current in it? carrying wire? • How is its direction defined? Power Source – coils of wire - compasses

33. Question • What is the direction of the magnetic field of a coil that has a current in it?

36. Demonstration • Bring compass • near each end • of a coil.

37. How is the magnetic field of a coil related to a magnet? • Like a bar magnet • But can be turned on and off

38. Quiz • Given the polarity • of the power source • and the direction the wire • is wound on the apparatus, • what is the direction of the magnetic field inside the coil? Power Source – wire coil on PVC pipe

39. 18.4 Magnetic ForcesonConductorsandMoving Chargespage 687

40. Demonstration • Force on • current carrying wire • in a • magnetic field Green power source, large magnet, swinging wire, support

41. Right Hand Rule B • Thumb • Direction of Current • Fingers • Direction of B-Field • Palm • Direction of Forcemagnetic Fmagnetic I

42. What is the direction of Fmag? F S N B F ? B ?

45. What will the loop do? N

46. Magnitude of the Force

47. Calculating the Force vector x vector = vector Dot Product Where θ is the angle between the B-field and the current.

48. Units of Magnetic Field • Thus k has a value of 1 • if one uses these units.

49. Demonstration • Force on Parallel Current Carrying Wires • 1. Current in same direction Power Source, 2 swinging wires, support