Impedance (Z) of a series L−C−R circuit is given as Z‌‌=√R2+(XL−XC)2 ‌‌=√R2+(ωL−‌
1
ωC
)2 ⇒‌‌Z‌‌=√R2+(2πfL−‌
1
2Ï€fC
)2 At XL=XC , then from Eq. (i), Zmin=R , and f=f0‌‌[f0= resonance frequency] Hence, the variation of Z with frequency f in a series L−C−R circuit is givenas