# Resonant Frequency

The** Resonant frequency** condition arises in the series circuit when the inductive reactance is equal to the capacitive reactance.

If the supply frequency is changed the value of X_{L} = 2πfL and X_{C} = 1/2πfC is also changed. When the frequency increases, the value of XL increases, whereas the value of XC decreases. Similarly, when the frequency decreases, the value of X_{L} decreases and the value of X_{C} increases.

Thus to obtain the condition of series Resonance, the frequency is adjusted to fr, point P as shown in the curve below. At point P when (XL = XC) the resonant frequency condition is obtained.

At series resonance, when XL = XC

Where, fr is the resonant frequency in hertz when inductance L is measured in Henry and capacitance C in Farads.