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)?

Assess. State – Assess. State – Due Friday, 1/16/15

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

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

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

Peak voltage

Peak Voltage

Peak Current

Power in an AC Circuit

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:

rms Voltage

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

Transformers--quantified

Transformers--continued

Example:

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