1. Alternating-Current Circuits
Chapter 33
Alternating-Current Circuits

2. AC Sources Voltage varies with time
Period (T)—time it takes to cycle once
Units of seconds
Frequency (f)—number of complete cycles per second
Units of Hz, 1/s
Angular frequency ()—rate at which the generator producing the voltage is spinning
Units of rad/s

3. RMS Voltage Average value of voltage over one cycle is zero
Voltage and current are described by the root-mean-square (RMS) value
Square the function
Take the average value
Take the square root

4. Inductors in AC circuits
Current is constantly changing in an AC circuit
Inductors fight a change in current
The higher the frequency, the faster the current changes, and the more the inductor fights back
Inductive reactance (XL)—effective resistance of an inductor
Units of Ohms ()
Dependent on the frequency of the signal
For a simple L circuit

5. Capacitors in AC Circuits
Capacitors do not represent a true break in an AC circuit
Since current changes direction, capacitors do not stop the flow
Capacitors will resist more as they charge up, the longer the current stays in one direction
Capacitive Reactance (XC)—effective resistance of the capacitor
Units of Ohms
Inversely proportional to frequency of current
For a simple C circuit

6. RLC Circuits
When a resistor, inductor, and capacitor are hooked in series, total resistance to current flow is called impedance (Z)

7. RLC Circuits
Voltage and current do not reach max values at the same time due to the capacitor and inductor
Sine curves are out of phase by an angle (), called the phase angle
When  is negative, voltage trails the current
When  is positive, voltage leads the current
When  is 0, they are in phase, and current is at its maximum possible value for that voltage
Frequency at which this occurs is called the resonant frequency

8. Phase relationships Purely resistive circuits
 = 0
Purely capacitive circuits
 = -90
Purely inductive circuits
 = 90
RC Circuits
 = negative, between -90 and 0
RL Circuits
 = positive, between 0 and 90
RLC Circuits
 = negative if XC>XL
 = positive if XC<XL
 = zero if XC = XL