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Magnetism

Magnetism. I. Current inwards. Current outwards. Lines of force. Right Hand Grip Rule. Not a Radial Field. Magnetism. Motion. Current. Field. Fleming’s Left Hand Rule. Left-for-Lift. Magnetism. Generalisation of the effect on any given current carrying wire

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Magnetism

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  1. Magnetism I Current inwards Current outwards Lines of force Right Hand Grip Rule Not a Radial Field

  2. Magnetism Motion Current Field Fleming’s Left Hand Rule Left-for-Lift

  3. Magnetism Generalisation of the effect on any given current carrying wire near a magnet is given by: Magnetic Field Strength (B) B = F / IL Where B, I and F are all mutually perpendicular. Unit of B = Tesla [T] 1 T = 1 N/Am

  4. Magnetism  F = BILSin 

  5. Magnetism F = Min F = 0 F = Max F = BIL

  6. B C A D

  7. Charged particle

  8. F = Bev

  9. A duck flying due North at 15 m/s passes over Atlanta, where the Earth’s magnetic field is 5 x 10-5 T in a direction 60 º below the horizontal line running north and south. If the duck has a net positive charge of 0.04 C,what is the direction and magnitude of the magnetic force upon it?

  10. v North q 60º 30º F = Bqv = 26 pN B 5 x 10-5 T West

  11. Magnetism r Near a long straight current carrying wire. B = 0 I / 2r 0 = permeability of free space = 4 x 10-7 NA-2

  12. What is the magnetic field strength and direction exactly half-way between the two wires? 10A 5A 10-5 T Into the board. 0.2 m

  13. Magnetism The Solenoid

  14. Magnetism South North The Right Hand Grip Rule The Solenoid

  15. Magnetism On the axis near the centre of the solenoid: B = 0nI n = Number of turns / length of solenoid

  16. B = 4.24 mT South You are looking through a solenoid that is 80 cm long with 900 turns and a radius of 2.5 cm. If it carries a current of 3 A calculate the magnetic field along the axis inside the solenoid. Which pole is the closest to you?

  17. Magnetism Motion Current Field Right Hand Grip Rule Left-for-Lift Fleming’s Left Hand Rule Summary of magnetism’s equations and rules: B = F / IL Near a long straight current carrying wire. B = 0 I / 2r On the axis near the centre of the solenoid: B = 0nI

  18. Electromagnetism Flux  = BA Unit = The Weber [Wb] Lines of flux

  19. Magnetism V V Faraday’s Law An EMF is induced in a conductor if there is any change in the flux. Flux linkage can change: or Flux cutting can occur:

  20. Magnetism Faraday’s Law continued... The magnitude of the induced EMF is proportional to the rate of change of flux linkage or rate of flux cutting. EMF = N / t And is always established so as to oppose its creation. (Lenz’s Law)

  21. Magnetism Motion Current Field Fleming’s Right Hand Rule

  22. Rectangular Solenoid B = 0.5 T t = 0.8 s 18 cm A 18 cm Number of turns = 200 R = 2  B = 0 T t = 0 s How much current flows while the field is changing? 2 A

  23. I a) What is the direction of the induced current through R?

  24. b a b) What is the direction of the current induced in R when S is closed: a  b, or b  a?

  25. c) What is the direction of the induced current in R when the current decreases rapidly to zero?

  26.                                                                                                                         v d) What is the direction of the magnetic field, that this copper rod is moving through? + _

  27. V Back EMF () Motor effect inhibited by induction effects. North South

  28. The Transformer Vp / Vs = Np / Ns

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