Today’s agenda: Induced emf. Faraday’s Law. Lenz’s Law. Generators. You must understand how changing magnetic flux can induce an emf, and be able to determine the direction of the induced emf. Faraday’s Law. You must be able to use Faraday’s Law to calculate the emf induced in a circuit. Lenz’s Law. You must be able to use Lenz’s Law to determine the direction induced current, and therefore induced emf. Generators. You must understand how generators work, and use Faraday’s Law to calculate numerical values of parameters associated with generators. Back emf. You must be able to use Lenz’s law to explain back emf.

Induced emf: an overview An emf is induced in a conductor moving in a magnetic field. Your text introduces four ways of producing induced emf. 1. Flux change through a conducting loop produces an emf: rotating loop. B start with this A  side view derive these

2. Flux change through a conducting loop produces an emf: 2. Flux change through a conducting loop produces an emf: expanding loop. v B B start with these                                     ℓ                         dA x=vdt derive these

3. Conductor moving in a magnetic field experiences an emf: 3. Conductor moving in a magnetic field experiences an emf: magnetic force on charged particles. start with these v B B   –                                   ℓ                         + derive this This is called “motional” emf, because the emf results from the motion of the conductor in the magnetic field. The other three examples in this lecture are “induced” emf because they involve the change of magnetic flux through a current loop, as described by Faraday’s Law.

4. Flux change through a conducting loop produces an emf: moving loop. start with this  derive these