Electro magnetic Induction (ch 21) We’ll cover ch 21.1 – 21.4 EM Induction is where we get all this electricity stuff. (w/out induction there would be no ipods, cell phones, video games)

EM Induction Michael Faraday found that a changing magnetic field creates an induced current in a coil of wire. A changing magnetic field induces an emf (emf = a voltage and hence a current) This induced emf is created when the magnetic field is moving relative to the conductor.

EM Induction Magnetic Flux is the amount of magnetic field crossing a given area Φ = BAcosΘ = magnetic flux A = area, B = magnetic field, and the angle is measured from the line (axis) perpendicular to A with the B field. (Flux is a maximum when it crosses the area perpendicular)

EM Induction Faraday’s Law for induction: the amount of emf produced depends on the change in flux per time. EMF (or voltage) = -Δφ/Δt = -ΔBAcosΘ/Δt To create an EMF(voltage) you can change either the magnetic field B, the area A, or the angle (like rotating a magnetic inside a conductor).

EM Induction Direction of the induced emf The current induced is directed to create its own magnetic field which will oppose the changing flux which is inducing it (huh?) In other words, the current induced will always make a magnetic field which tries to keep things the way they were. (oh, that’s much clearer)

EM Induction If the conductor is a coil of wire with N loops, then the emf=-NΔφ/Δt.

EM Induction For a moving conductor crossing a magnetic field, there is one more relationship on the $50,000 green sheet It can be shown (look on page 590) that emf = Blv where B = magnetic field, l = length of wire crossing the field, v = velocity of that length of wire crossing the field.