The current in a series RCL circuit is given byI = V / Z = Notice that this has a maximum value for

X _{L}= X_{C}since the (X

_{L}- X_{C}) term in the denominator vanishes for X_{L }= X_{C}. From earlier equations for X_{L}and X_{C}, this means2 f L = Consider the capacitance and inductance to be fixed for a given circuit while the frequency can be varied. The current will be a maximum for the frequency that fits this equation; solving for the frequency and labeling it f

_{o}, we havef _{o}=f

_{o}is known as theresonance frequencyof the circuit. Atresonance frequencyin an electrical system, the amplitude of the current becomes maximum. This corresponds to resonance in mechanical systems in which the amplitude of vibration becomes maximum at the resonance frequency.(c) Doug Davis, 2003; all rights reserved

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