1. Physics 12 Mr. Jean December 10 th, 2013

2. The plan: Video Clip of the day –http://www.youtube.com/watch?v=bI7AUgp5f PIhttp://www.youtube.com/watch?v=bI7AUgp5f PI DC Motors AC Motors DC Generators & AC Generators Transformers

3. Problems with DC Power: 1. The magnetic forces are aligned directly opposite each other and will no longer experience a torque. –If you could change the direction of the current, the coil would again experience a torque. 2. If the coil keeps turning, the leads will twist and eventually break.

6. AC Electric Motor Uses slip rings as commulator. Since the current is alternating, the motor will run smoothly only at the frequency of the sine wave. The magnetic field is sinusoidally varying, just as the current in the coil varies.

8. AC Motors: http://www.youtube.com/watch?v=_- WQZ1SGqi4http://www.youtube.com/watch?v=_- WQZ1SGqi4

9. AC Electric Motor Uses slip rings as commulator. Since the current is alternating, the motor will run smoothly only at the frequency of the sine wave. The magnetic field is sinusoidally varying, just as the current in the coil varies.

11. To view on your own time: Introduction to DC Power & Motors: http://www.youtube.com/watch?v=OpL0jo qJmqYhttp://www.youtube.com/watch?v=OpL0jo qJmqY

12. AC vs. DC Motors: Electric motors are mostly AC because our electric energy for industry and home is transmitted as AC. DC motor – starter motor on a car.

13. AC Generators: Generators are essentially the same design as motors. –The mechanical energy input to a generator turns the coil in the magnetic field. This produces an emf (voltage). A sinusoidal voltage output. The mechanical energy may come from: –i. Steam –ii. Wind –iii. Waterfall

15. DC Generator: The commutator must change the AC flowing into its armature into DC. Commutators keep the current flowing in one direction instead of back and forth.

17. Power Production Generators were built by Tesla to generate electricity reliably and in large quantities. Most of today’s energy sold is in the form of AC because it can easily be transformed from one voltage to another.

18. High Voltage with Low Current: Power is transmitted at high voltages and low current without much energy loss (heating of wire) because it can be stepped down from the plant to many cities, to a city, to the household. Household typical outlet is 120 V AC.

19. Transformers: Transformers are used to transfer energy from one circuit to another by means of mutual inductance between two coils.

20. Types of Transformers: Transformers consist of a primary coil (input) and a secondary coil (output). Step-up Transformer –Secondary has more turns –greater electric potential (V) induced, caused by the lowering for current (I)

21. Types of Transformers: Transformers consist of a primary coil (input) and a secondary coil (output). Step-down Transformer –primary has more turns –Thus less electric potential (V) induced causing a greater current (I).

22. Transformers: Transferring energy from one coil to the other OR the rate of transferring energy is the power. The power used in the secondary is supplied by the primary. LAW OF CONSERVATION OF ENERGY

24. Transformers: Brightstorm: Transformers –http://www.youtube.com/watch?v=4aYhAbzS wvshttp://www.youtube.com/watch?v=4aYhAbzS wvs

25. To do: Work on Reviews Continue to read –You should have read chapters 15 & 16 at this point –Always read through the blue shaded examples because these examples are very similar to much of the work we do in class.