1. April 26 th, 2006 AC Circuits PHYS 102 Where T is the period of oscillation.

2. April 26 th, 2006 AC Circuits PHYS 102 Transformers: One symbol used to denote a transformer is:

3. April 26 th, 2006 AC Circuits PHYS 102 Transformers: Looks like two solenoids in close proximity to one another.

4. April 26 th, 2006 AC Circuits PHYS 102 Transformers: V P = N P (Induced EMF); V S = N S (Induced EMF); same induced EMF Called step-up transformer Called step-down transformer If primary current is alternating in time, then the magnetic flux in transformer core is changing! Induced EMF

5. April 26 th, 2006 AC Circuits PHYS 102 Transformers: Remember: Power input must equal power output (Always)

6. April 26 th, 2006 AC Circuits PHYS 102 Transformers: Have we all seen a transformer?

7. April 26 th, 2006 AC Circuits PHYS 102 How do the other circuit elements behave under the influence of an AC source? Remember, everything in the past has been analyzed with a DC source.

8. April 26 th, 2006 AC Circuits PHYS 102 Resistors: We say that the current is “in phase” with the driving voltage.

9. April 26 th, 2006 AC Circuits PHYS 102 Capacitors: We say that the current is “out of phase” with the driving voltage. Current in a capacitor leads the voltage by 90 o.

10. April 26 th, 2006 AC Circuits PHYS 102 Capacitors: X C is called the “reactance” of a capacitor. Units = Ohms. The slower the frequency the greater the capacitive reactance. Low frequencies→ capacitor acts like open circuit. High frequencies→ capacitor acts like short circuit. Resembles current through resistor. Since the sine function has a maximum value of 1, we could define a peak current.

11. April 26 th, 2006 AC Circuits PHYS 102 Capacitors: X C is not the same as Resistance because no power is dissipated through a capacitor. Current leads driving voltage: it takes current to move charge on the capacitor plates→current must flow before the voltage can change significantly.

12. April 26 th, 2006 AC Circuits PHYS 102 Inductors: We say that the inductor current is “out of phase” with the driving voltage. Current in an inductor lags behind the voltage by 90 o.

13. April 26 th, 2006 AC Circuits PHYS 102 Inductors: X L is called the “reactance” of an inductor. Units = Ohms. The greater the frequency the greater the inductive reactance. Low frequencies→ inductor acts like short circuit. High frequencies→ inductor acts like open circuit.