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An inductor of 10 mH and a capacitor of 16 microF are connected in a circuit (see figure). The supply frequency equals the circuit's resonant frequency. Which ammeter reads zero current?
- A1
- A2
- A3
- none
Correct answer: A3
Solution
At resonance the parallel LC (tank) circuit has the inductive and capacitive branch currents equal and opposite, so they cancel and the net current taken from the source is (ideally) zero. The ammeter placed in the supply/main line of the parallel combination therefore reads zero, while the branch ammeters still read large circulating currents. That main-line ammeter is A3.
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