1.

An alternating current is flowing through a series LCR circuit. It is found that the current reaches a value of 1 mA at both 200 Hz and 800 Hz frequency. What is the resonance frequency of the circuit ?

Answer»

600 Hz
300 Hz
500 Hz
400 Hz

SOLUTION :Since the alternating CURRENT is flowing through a series LCR CIRCUIT.
For maximum value of current
`omega L-(1)/(omega C)=0`or`omega L=(1)/(omega C) ""`…..(i)
Resonance frequency of series LCR ciruit is
`omega = (1)/(sqrt(LC))` From (i),`200 L=(1)/(800 C) ""` [`because` current reaches a value of 1 mA]
or `(1)/(LC)=200xx800` or `(1)/(sqrt(LC))=sqrt(200xx800)=400 Hz`


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