Faraday’s Law of Induction Magnetic flux  = A B cos   B A A changing magnetic flux generates an induced voltage (emf = electromotive force) V = [emf] = - N  /  t  = (ABcos  ) final – (ABcos  ) initial

Voltage induced in a moving conductor V max = [emf] = -Blv Length Velocity Motional EMF Induced emf depends on angle between the Magnetic field and the velocity direction.

Lenz’s Law An induced emf gives rise to a current whose magnetic field opposes the original change in flux new, larger B Induced B Induced current

Lenz’s Law Exercises

Applications of Faraday’s Law Eddy Currents Transformer: Primary and secondary coils Iron yoke (to contain flux) AC voltages only ! No loss -> Input power = output power V 2 N 2 I 1 V 1 N 1 I 2 == Electric Generator: Alternating (AC) voltage  = BA cos(  t) angular velocity  = 2  f t V t 

Electromagnetic Waves 000 Speed of light (Constant of Nature) c = m/s (3 x 10 8 m/s) Also: c = frequency times wavelength c = f