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Electromagnetic induction

Electromagnetic induction. Topic 12. Remember?. An electron is moving downward with a velocity, v, in a magnetic field directed within the page, determine direction of force. Moving conductor. Conductors contain free electrons

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Electromagnetic induction

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  1. Electromagnetic induction Topic 12

  2. Remember? • An electron is moving downward with a velocity, v, in a magnetic field directed within the page, determine direction of force.

  3. Moving conductor • Conductors contain free electrons • So when a conductor moves downward, electron will experience a magnetic force pulling them to the left. • Lattice atoms on the right become positive… • There is a potential difference now

  4. Moving conductor • E force produced wanting to push electrons to the right • Forces are now balanced and electrons will stop moving • What will happen if you connect a resistor to the metal conductor?

  5. Moving conductor R – – – + + + • E force produced wanting to push electrons to the right • Forces are now balanced and electrons will stop moving • What will happen if you connect a resistor to the metal conductor? • Current will flow from high to low potential

  6. Moving conductor R – – – + + + • What did we define emf previously as? • Amount of chemical energy converted to electrical energy per unit charge

  7. Moving conductor R – – – + + + • What did we define emf previously as? • Amount of chemical energy converted to electrical energy per unit charge • We don’t have chemical energy here!!! • Where does our energy come from here?

  8. Moving conductor R – – – + + + • Which direction were we pushing this conductor? • Another force acting on conductor?

  9. Moving conductor R – – – + + + • Which direction were we pushing this conductor? • Another force acting on conductor? • Yes magnetic force… which direction is it acting?

  10. Moving conductor Magnetic force R – – – + + + • Which direction were we pushing this conductor? • Another force acting on conductor? • Yes magnetic force… which direction is it acting? – upward • So when you’re pushing it downward, what energy is it gaining? Force applied

  11. Moving conductor Magnetic force R – – – + + + • Which direction were we pushing this conductor? • Another force acting on conductor? • Yes magnetic force… which direction is it acting? – upward • So when you’re pushing it downward, what energy is it gaining? – EPE • You are doing work • If forces are equal, conductor is moving at constant v. Force applied

  12. Moving conductor Magnetic force R – – – + + + • EPE will be converted into heat • Energy is conserved • Now let’s define INDUCED EMF? • Amount of mechanical energy converted into electrical energy per unit charge. Force applied

  13. Calculating induced EMF • Maximum p.d. in conductor is when the magnetic force ON ELECTRON is equal to the electrical force L –

  14. Calculating induced EMF • Maximum p.d. in conductor is when the magnetic force ON ELECTRON is equal to the electrical force • Electron will stop moving.. Therefore greatest p.d. • Equate equations L –

  15. Induced EMF equation * * The induced EMF will be the same as p.d. across conductor

  16. Question • If magnetic field not perpendicular to direction of motion… what will you do? B v

  17. Question • If magnetic field not perpendicular to direction of motion… what will you do? • Take the B that is perpendicular to v

  18. QUESTION

  19. QUESTION

  20. THREE HAND RULES RIGHT LEFT

  21. Faraday’s law • What generated induced emf? • What did it depend on?

  22. Faraday’s law • What generated induced emf? – moving conductor in a magnetic field • What did it depend on? • Faraday’s law: • The induced emf is equal to the rate of change of flux

  23. Flux VS flux density • Let’s look at this analogy

  24. Flux VS flux density • How much grass do you have? • Is it taking lots of area?

  25. Flux VS flux density • Pieces of grass is flux density (B) • Area over which grass takes over is flux (Φ)

  26. Flux VS flux density Flux unit: Tm2, Wb

  27. Flux VS flux density • If area at angle from B • Find component of B that will be perpendicular to area Normal to surface θ

  28. Lenz’s law • Moving conductor in magnetic field causes a force to oppose the direction of motion as seen earlier (if not true than energy will not be conserved) • Lenz’s law is an extension to Faraday by stating that: • the induced current will be in such a direction as to OPPOSE THE CHANGE IN FLUX that created the current.

  29. Question

  30. Question

  31. Question • Determine direction of current

  32. Question

  33. Question

  34. Question

  35. Question

  36. Question • Rail gun… how does it work? resistor

  37. Question • What will happen if you remove the magnetic field suddenly? resistor

  38. Question • BRING BACK THE FIIIEEEELLLDDD!!! LENZ’S LAW resistor

  39. Question • to get the field back, which direction should the induced current be? resistor

  40. Question • Current upward…. Force???? resistor

  41. Question • Current upward…. Force to the right… and off it goes….. resistor

  42. Question

  43. Question http://science.howstuffworks.com/rail-gun1.htm

  44. Read • Applications of EM induction on page 213

  45. Alternating current (AC) • What’s the difference between a motor and a generator?

  46. Alternating current (AC) • What’s the difference between a motor and a generator? • Motor  electrical to mechanical energy • Generator  mechanical to electrical

  47. Alternating current (AC) • What’s the direction of current induced here?

  48. Alternating current (AC) • What’s the flux going to be at angle 0?

  49. Alternating current (AC) • What’s the flux going to be at angle 0? • Maximum since • So how will the graph look like?

  50. Alternating current (AC) Label the positions in graph

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