Physics 123

21. Electromagnetic Induction 21.1 Induced EMF (voltage) 21.2 Faraday’s Law - Lenz’s Law 21.3 EMF induced in a moving conductor 21.4 Changing magnetic flux produces E 21.5 Electric Generators 21.7 Transformers

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

Faraday’s Law of Induction Induced emf equals the rate of change of magnetic flux Voltage = change of flux / time V = B A / t

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

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

EMF induced in a moving conductor X X X X X X

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

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 T Voltage = B Lv V = 5 x x 280 m/s x 70 V = 1.0 volt

Changing magnetic flux produces E X X X X X X V = B L v E L = B L v E = B v

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

Transformer I I B I I B Primary Secondary V p = N p B A / t V s = N s B A / t V s / V p = N s / N p

That’s all folks!