Combinations-Resistive & Reactive

A resistive circuit opposes current directly. A reactive circuit transforms current and creates opposition to current flow in the process. For example, when current flows through an inductor, each winding creates an electromagnetic field. These electromagnetic fields interact with one another, creating an overall induced field that we can observe as measurable voltage. This interchange of energies between the windings of the coil creates an opposition to the flow of current called "inductive reactance."

Similarly, a capacitive circuit will create an opposition to current flow. The capacitor reacts to current flow and creates an electric field that is measurable as voltage. The resultant opposition to current flow is called "capacitive reactance."

When a circuit has a combination of these element, resistors, capacitors, and inductors, the calculation of the total impedance to current flow is calculated by the formula:

Z equals the square root of the resistance squared plus the difference of the capacitive reactance and the inductive reactance squared.


Z = total impedance in ohms
R = resistance of the circuit in ohms
XC = Capacitive reactance of circuit in ohms
XL= Inductive reactance of circuit in ohms

Find the current flowing to an electric motor operated at 240 volts that has an electrical resistance of 80 ohms, an inductive reactance from the motor windings of 90 ohms, and a capacitive reactance from a connected capacitor of 30 ohms. You cannot find the total impedance by adding the resistance and reactance together since they are not in phase. Use the equation for calculating the total impedance. The square root of 80 squared + ( 30 squared - 90 squared equals a total impedance of 100 ohms. Use ohms law to find the current flow by dividing 240 volts by 100 ohms and the current flow equals 2.4 amps.