RESONANCE
Resonance in an AC circuit is when the oppposition to current flow is least, i.e. when the impedance is lowest, this happens when X_L = X_C. As both of these depend on the frequency of the circuit, a point of resonance can be found by adjusting the frequency. At resonance frequency 2 π f L = ¹ / _{2 π f C} hence f = 1 / _{2 π SQR( L C )}