Fig. 1. shows a resonance bridge, consisting of a series resonance circuit.

Fig. 1. The resonance bridge circuit

The resonance circuit is consisted by *R*_{4}, C_{4}, and *L*_{4} in series.

All the others arm consist of resistor only.

Using the bridge balance equation , we have , *Z*_{ab}Z_{cd}=Z_{bc}Z_{ad ,}

Substituting the values in the balance equation, we get,

Equating real and imaginary terms, finally we get,

Resonant frequency,

This bridge can be used to measure unknown inductances or capacitances.

1. If an inductance is being measured, a standard capacitor is varied until balance for resonance is obtained.

2. If an capacitance is being measured, a standard inductance is varied until balance for resonance is obtained.