Electromagnetism Physics 100 Chapt 15 Michael Faraday

General circuit + - Appliance + - Energy source (device that separates + & - charge) I I

Moving a Conductor in a B-field separates + & - charges I

Use this to drive an electric circuit + + I + + +

Moving wire loop in a B field + + v An electric current is “induced” in the loop

Either the magnet or the loop can move + + v an electric current is “induced” in the loop

Magnetic flux (  ) thru a loop  = BA ┴

Flux thru a coil of N loops  = N BA ┴

Faraday’s law change in N BA ┴ elapsed time Induced voltage in a circuit = change in  elapsed time EMF = “Electro-Motive Force” Michael Faraday

Rotating coil in B field A ┴ = 0   =0 B

Rotating coil in B field A ┴ = A coil   = maximum B

Rotating coil in B field A ┴ = 0 (again)   = 0 B

AC voltage

Lenz’ Law v v B B + + N S the fall produces an induced current the B-field produced by the induced current tries to impede the fall B-field from induced current I

Lenz’ law An induced voltage always gives rise to an electric current that creates a magnetic field that opposes the influence that produced it.

Maglev trains

Maglev