Reactance, Impedance, and Power Formulas for Sinusoidal Circuit
These are the formulas used when other then Direct current is involved in a circuit. Both inductors and capacitors effect the phase of the current and voltage and this shift in phase needs to be taken into account when determining the impedance and power of a circuit. Included is also the formula for efficiency, to determine if what your putting in is worth what your getting out.
The above formulas are used in AC(alternating current) circuits.