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Parallel Resonant CircuitsAuthor: J.B. Hoag Fig. 6 B shows a parallel circuit and its impedance curves.
The curves are of the same shape as the current curves of a series circuit. Note that the impedance across the terminals of a parallel circuit is a maximum at resonance,^{1} whereas it is a minimum for the series circuit. The current in the LCR circuit itself is often very large at resonance and can cause considerable heating. The impedance of a parallel circuit at resonance is given by
if all the resistance is in the coil (which is very nearly true in practice). The meaning of Q is given in Section 6.4. The resonant frequency f_{r }is given by the same equation as for a series circuit provided R is small in comparison with X. This is often true in radio frequency circuits.


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