# At resonance why the coupled impedance is pure resistance in a double tuned circuit...!!

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#### Himanshoo

Joined Apr 3, 2015
265
The following discussion is about double tuned circuit and its operation at resonant and non resonant (low and high) frequencies....

Generally at series resonance the reactive impedance cancels each other hence resulting in maximum current, while in parallel circuit the current flowing in two branches of the circuit cancels each other, so technically saying there is no current flowing in the circuit and can be thought as a high impedance occurring in the circuit.

Now at frequencies other than resonance a reactive coupled impedance is reflected to the primary and cancels the reactive impedance of the primary which results in minimum impedance in primary causing large current to flow.
While at resonance the impedance that is coupled to primary is purely resistive in nature. So at resonance the primary resistance is maximum and there is a dip in the double hump curve.
But now my question is that at non resonant frequencies why does resistance is not coupled or why do they do not consider it to be coupled by the secondary into the primary since resistance is present every time as it is the property of the material .??
or
It can be said like....why at non resonant frequencies resistance do not get coupled to the primary circuit as at resonant frequencies only pure resistance get coupled from the secondary and increases the primary resistance....

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