Place a resistor and inductor in series with an AC source. What's the current?

Once again, to find the impedance (the equivalent resistance) we add the individual resistances as vectors. Resistors want the voltage and current to be in phase, while inductors want the voltage to lead the current by 90^o. Again the two vectors are perpendicular, with the effective resistance of the inductor in the opposite direction from the way the effective resistance of the capacitor went.

Let's say we know the resistance R, inductance L, and frequency f. To find the current follows these steps:

• Find the inductive reactance of the inductor: X_L = wL, where w = 2pf
  
  
• Find the impedance of the circuit: Z² = [R² + X_L²]
  
  
• Find the current from V = IZ.
  
  
• Find the phase angle:

  tan(f)

  =

  XL R