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Passive Filters - Engineering

Q1:

A series resonant band-pass filter consists of a 2 mH coil, a 0.005 F capacitor, and a 120  resistor. The winding resistance of the coil is 12 . The output voltage is taken off the resistor. Input voltage is 12 Vrms. What is the output voltage magnitude at the center frequency (f0)?

A 10.9 V

B 1.09 V

C 1.1 V

D 12 V

ANS:A - 10.9 V

We know that at series resonance inductive reactance = capacitive reactance. Therefore total impedance is only the net resistance of the circuit. Here the net resistance is = (120+12) =132 ohm.

So, current at the resonant condition = 12V/132 ohm = 0.09A.

As the output voltage is taken off the resistor, so the output voltage at center frequency is = (0.09*120) = 10.9V.