1. Chapter 22: Induction and Alternating Current pp 793 - 820

2. Essential Questions  How can current be produced without a power source?  How do motors work?  How is mechanical energy converted to electrical energy?

3. Objective(s): We will be able to…  Describe how a magnetic field can induce current in a wire.  Describe how an electric motor relates to an electric generator.

4. Agenda:  Sorry, no building motors today due to technical difficulties! Tomorrow instead.  Check and review Magnets homework.  Intro to Inductance:  Notes:  Magnetic Fields and Induced EMFs  Generators  Motors

5. Electromagnetic Induction  Current in a circuit can be induced without the use of a battery or voltage source.  We know that magnets cause electrons to move and realign, sooo…  If a magnet moves closer to a circuit…  Or a circuit is moved closer to a magnet…  If there is any relative motion between a circuit and a magnet, current is induced in the circuit.

6. Electromagnetic Induction  The angle between the magnetic field and the circuit affects induction.  (The blue dots are magnetic field lines coming out of the page)  The closer to perpendicular the magnetic field is to the circuit, the more current is induced.  The greater the amount of magnetic field lines (the strong the magnetic field), the greater the current induced. Not surprisingly.

7. Generators  As we learned before, generators convert mechanical energy into electrical energy.  For example, a hydroelectric plant converts falling water into rotational motion (like using a water wheel).  This rotational motion turns a wire loop in a magnetic field, inducing an emf.

8. Generators  Generators produce a constantly changing emf, due to the angle between the magnetic field and the wire (circuit) constantly changing.  This is what produces alternating current.  The frequency of rotation of the coil determines the frequency of the sign change of the emf.

9. Motors  Motors are devices that convert electrical energy to mechanical energy.  Like generators in reverse:  A current is run through a wire coil connected to a rotating shaft.  As that wire rotates, it will be alternately attracted and repelled by any magnet in its vicinity.

10. Recap  Any relative motion between a magnet and a circuit induces a current in that circuit.  The induced emf is greatest when the magnetic field is perpendicular to the circuit.  Generators convert mechanical energy to rotational motion, rotating a wire coil in a magnetic field.  Motors convert electrical energy to mechanical, using a magnet to repel and attract a wire coil repeatedly.

11. Homework  Due Friday:  p802 #2  p 821 #5, 15, 16, 22