Resistance is the obstruction/opposition in the flow of current . R = V/ I Reactance :- It is the opposition to the change in the flow of current in an alternating current circuit due to inductance and capacitance. Inductive Reactance Capacitive Reactance Reactance that occurs in an inductor is known as inductive reactance. Reactance that occurs in a capacitor is known as capacitive reactance. XL = inductive reactance (ohms) f = frequency (Hz) L = inductance (henrys) XC = capacitive reactance (ohms) C = capacitance (farads) IMPEDANCE Impedance is the combination of resistance and reactance (both inductive and capacitive) . It is a complex number, containing both real and imaginary parts. (The real part of impedance is resistance, while the imaginary part is reactance.) Z = magnitude of impedance (ohms) XT = total reactance (ohms) = XL – XC In phasor terms, impedance Z is represented as a combination of resistance R and reactance X as: X=R+jX Admittance Admittance is the reciprocal of impedance Y = 1/ Z