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Magnetism

Magnetism. Chatfield Senior High Department of Physics. Magnetism Definition. Property of spin of electrons in magnetic substances Permanent: (iron) Magnetite Alnico Magnetism can also be created by a electric current . Electromagnet. Earth’s Magnetic Field.

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Magnetism

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  1. Magnetism Chatfield Senior High Department of Physics

  2. Magnetism Definition • Property of spin of electrons in magnetic substances • Permanent: (iron) Magnetite Alnico Magnetism can also be created by a electric current

  3. Electromagnet

  4. Earth’s Magnetic Field

  5. Magnetic Field Line Rules • Field lines go from North to South • Field is strongest at the poles • No magnetic monopoles in nature

  6. Attraction and Repulsion of Magnets • Like poles repel • Unlike poles attract

  7. Right Hand Rule • Thumb points in direction of conventional current flow (+ to -) (Note this is different than electron flow which goes from – to + (Thanks Ben Franklin!) • Fingers point in direction of the magnetic field

  8. Right Hand Rule (Current going left)

  9. Right Hand Rule (Current going right)

  10. Magnetic Field Through a Curved Wire • Magnetic north is determined by the thumb, fingers encircle the direction of the current

  11. Application (Solenoid)

  12. Current Flow through two parallel wires • Current flows in same direction (attraction) • Current flows in the opposite direction (repulsion)

  13. If a current is flowing to the right in an uninsulated wire, the magnetic field is… • A. Going clockwise • B. Going counterclockwise • C. Going straight up • D. Cannot tell from the information given The answer is A

  14. If current goes clockwise through a solenoid, the north magnetic field points…. • A. To the right • B. To the left • C. Upward • D. Cannot tell from the information given The answer is A

  15. If current is traveling the same direction in two uninsulated parallel wires, the wires… • A. Attract • B. Repel • C. Remain the same • D. It is unpredictable The answer is A

  16. Transfers electrical energy to mechanical energy Motors

  17. Parts of a Motor • Commutator Armature Magnet Wires

  18. Commutator for AC and DC Circuits

  19. Left Hand Rule for Motors

  20. The Alternator

  21. Generator • Takes mechanical energy and transforms it into electrical energy

  22. Speaker • Try to describe how a speaker works

  23. Speaker • Permanent magnet • Coil of wire wound around the magnet • AC current goes through a coil and it causes the cone to vibrate

  24. Microphone • Now can you explain how a microphone works? (Hint: It is the opposite of a speaker)

  25. Tape Recorder / VCR

  26. Transformers! • Robots in Disguise!

  27. Electrical Transformers!

  28. Power Transmission

  29. How transformers work • Power is constant in both coils • You must have AC source for a transformer • Transformers can be step up (increases the voltage) or step down (decreases the voltage)

  30. Transformer Equation • P = VI • Power of primary coil = Power of secondary • P p = P s • V p I p = V s Is • V p = I s = N p V s I P N s Voltage is indirectly related to current and directly related to the winding of wires

  31. Transformer Problem • What is the current and the number of winding of wires in an electrical train set? • V p =120 V V s = 6 V N p =1000 windings I p = 1.5 A V I = V I (120) (1.5) = 6 I I= 30 A (or 20 times more) The number of windings goes down by a factor of 20 or 50 windings in the secondary coil

  32. Tokamak

  33. Princeton Plasma Physics Lab

  34. Yamanashi Maglev Train

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