Admittance (Y): Admittance is defined as the ability of the circuit to carry (admit) alternating current through it. It is the reciprocal of impedance Z. i.e Y = 1/Z. For parallel circuit consisting two branches having impedances Z1 and Z2 in parallel, the equivalent impedance of parallel combination is given by,
where, Y is the equivalent admittance of the parallel circuit Y1 and Y2 are the admittances of the two branches respectively.
If the equivalent impedance is expressed as
then the admittance is obtained as,
Susceptance is defined as the imaginary part of the admittance. It is expressed as,
In DC circuit, the reactance is absent, hence X = 0 and susceptance equals to zero.