1 Alternating Current and RLC Circuits Alternating Current: the current direction changes with time.  Compare with DC in which the current direction stays the same with respect to time, the magnitude of the current may change.  A typical case in AC: I = I MAX SIN(ωt). A power source normally is described as V = V MAX SIN(ωt).  Generation: rotating wire loops in magnetic field generate AC power. (demo: 32.18)  Main advantages: for power generation (actually the magnet turns) and transmission. Review: DC on RC and RL circuit, and now pay attention to the current/voltage relationship in time.  RC External torque turns the wire loop at an angular velocity ω. The magnetic flux through this loop is Φ B = B  A  COS(ωt) So the induced emf is When this emf is applied to a resistor, from Ohm’s Law, the current through this resistor is I = I MAX SIN(ωt), With I MAX = V MAX /R.

2 Alternating Current and RLC Circuits Review: DC on RC and RL circuit, and now pay attention to the current/voltage relationship in time.  RL RCL CurrentRise/fall w/ voltageLeads voltagelags behind voltage VoltageSame time w/ currentlags behind currentleads current

3 Alternating Current and RLC Circuits R, C and L in AC circuits:  R

4 Example An electric stove is specified as 6000W at 240V. If it is connected to an AC outlet in a laboratory. The AC outlet has a sticker reads V = 311SIN(100πt). What is heat the stove generates in 10 seconds?

5 Alternating Current and RLC Circuits R, C and L in AC circuits:  C

6 example The generator in an AC capacitor circuit creates a maximum potential difference across the 3.37×10 −6 F capacitor of 243 V. What is the amplitude of the alternating current if the frequency of the generator is (a) 455 Hz? (b) 1750 Hz?

7 Alternating Current and RLC Circuits R, C and L in AC circuits:  L

8 example The generator in an AC inductor circuit creates a maximum potential difference across the 2.74×10 −3 H inductor of 243 V. What is the amplitude of the alternating current if the frequency of the generator is (a) 455 Hz? (b) 1750 Hz?

9 Alternating Current and RLC Circuits Review of LC and beyond:  LC oscillator  Energy in LC oscillator

10 Alternating Current and RLC Circuits Review of LC and beyond:  LC in AS circuits.

11 Alternating Current and RLC Circuits Add R to LC: RLC in AC circuits