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Physics 223

Physics 223. 31. Faraday’s Law. 31.1 Faraday’s Law of Induction 31.2 Motional EMF 31.3 Lenz’s Law 31.4 Induced EMF and Electric Fields 31.5 Generators and motors. B. I. I. N. S. Magnetism produces current. Magnet thrust into the coil. 31.1 Faraday’s Law of Induction.

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Physics 223

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  1. Physics 223

  2. 31.Faraday’s Law 31.1 Faraday’s Law of Induction 31.2 Motional EMF 31.3 Lenz’s Law 31.4 Induced EMF and Electric Fields 31.5 Generators and motors

  3. B I I N S Magnetism produces current Magnet thrust into the coil

  4. 31.1 Faraday’s Law of Induction Induced emf equals the rate of change of magnetic flux Voltage = change of flux / time ɛ = - dB /dt EZ does it! V = B A / t

  5. X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X EMF induced in a moving conductor

  6. X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X EMF induced in a moving conductor V = B A / t V = B L d / t V = B L v

  7. What is the voltage across the wing tips of an airplane? wingtips = 70 m apart speed = 1000 km/h and Earth’s B = 5 x 10- 5 T Voltage = B Lv V = 5 x 10- 5 x 280 m/s x 70 V = 1.0 volt

  8. B B I I I I N N S S 31.3 Lenz’s Law The induced current will oppose the original change in flux

  9. I I I I Lenz’s Law B increasing B decreasing Old wine … New bottle!

  10. X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X 31.4 Induced EMF and Electric Fields V = B L v E L = B L v E = B v

  11. 31.5 Electric Generator V = B L v sin  V = B L d  sin  V = B A  sin t V = B A N  sin t

  12. Hybrids: Regenerative Braking! When you slam on the brakes, energy is not lost to friction, as in the good old days, but is recouped as the motor acts as a generator and stores the energy in the battery!

  13. B B I I I I Primary Secondary Transformer Vp = Np B A / t Vs = Ns B A / t Vs / Vp = Ns / Np

  14. That’s all folks!

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