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 magn
itude of the current may change. A typical case in AC: I = IMAXSIN(ωt). A power source normally is described as V = VMAXSIN(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
)t(V)t(BAdt
d B SINSIN max
External torque turns the wire loop at an angular velocity ω. The magnetic flux through this loop is
ΦB = BACOS(ωt)
So the induced emf is
When this emf is applied to a resistor, from Ohm’s Law, the current through this resistor isI = IMAXSIN(ωt), With IMAX = VMAX/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
R C L
Current Rise/fall w/ voltage Leads voltage lags behind voltage
Voltage Same time w/ current lags behind current leads 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
Top Related