Alternating Current and RLC Circuits

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 IMAXSIN(?t). A power
  source normally is described as V VMAXSIN(?t).
• 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 ?. The magnetic flux through this loop
is FB B?A?COS(?t) So the induced emf is
When this emf is applied to a resistor, from
Ohms Law, the current through this resistor is I
IMAXSIN(?t), 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(100pt). 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
  3.3710-6 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
  2.7410-3 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