Impedance:

• The impedance Z of a circuit is defined as the ration of phasor voltageand phasor current. The impedance is expressed as the sum of resistance and reactance. For a pure resistor, the impedance is Z is equal to R, for a pure inductance (internal resistance is zero or considered negligible for small values), the impedance Z is equal to the inductive reactance XL and for the pure capacitance, the impedance Z is equal to the capacitive reactane. Impedance is expressed by 

For resistor only        Z=R,         
For inductor only        
For capacitor only        

• For series resistor and inductor, series resistor and capacitor and series resistor, inductor and capacitor, the impedances are expressed as shown in figure 1.9

Diagram coping problem

Fig. 1.9 impedance in series connection of passive components