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Electro magnetic Induction (ch 21)

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.

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Electro magnetic Induction (ch 21)

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  1. 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)

  2. 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.

  3. 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)

  4. 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).

  5. 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)

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

  7. 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.

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