1. Warm-up—1/15/14 What happens when you rotate a coil of conductive material through a uniform magnetic field (not just move it linearly)?

2. Assess. State. 12.2.1 – 12.2.9 Assess. State. 12.3.1 – 12.3.5 Due Friday, 1/16/15

3. AC Generator As the ring rotates within the magnetic field, what happens?

4. AC generators Video link (it’s old…and if you watch the whole thing, it’s long, but it’s good)—we’re just going to watch the first few minutes today http://www.youtube.com/watch?v=LisefA_YuVg&safe=active

5. In a nutshell… DC generators—use a split-ring commutator to ensure that the direction of the induced emf (and resulting current) is always in the same direction upon output from the generator AC generators—use a set of slip rings to provide constant contact with the brushes, resulting in an induced emf and current that are alternating in magnitude and in direction

6. Peak voltage

7. Peak Voltage

8. Peak Current

9. Power in an AC Circuit

10. Power is always a positive value, and will be equal to zero Watts every half rotation of the coil. Average power is ½ the peak power:

11. rms Voltage

13. Transformers A tool used to take advantage of the fact that an alternating current generates an alternating magnetic flux in a coil. An iron core connects two separate coils Primary coil  the coil that is the “input” to the transformer Incoming alternating current generates an ever-changing flux Secondary coil  the coil that delivers the “output” Because of the iron core, the flux from the primary coil induces an emf in the secondary coil and, therefore, a current

14. Transformers--quantified

15. Transformers--continued

16. Example:

17. Step-down and Step-up Transformers Step-Down: A transformer designed to have a high input voltage and a low output voltage There will be fewer loops in the secondary coil Step-up: A transformer designed to have a low input voltage and a higher output voltage More loops in secondary coil