Question

In a series $L-C-R$ circuit, current in the circuit is $11A$ when the applied voltage is $220V$. Voltage across the capacitor is $200V$. If value of resistor $20\Omega$, then the voltage across the unknown inductor is

• A. Zero
• B. $200V$
• C. $20V$
• D. None of these

Answer 1

The correct option is B $200V$

The given LCR circuit is in resonance. Inductive reactance magnitude $X_L$ increases as frequency increases while capacitive reactance magnitude $X_C$ decreases with the increase in frequency. At one particular frequency, these two reactances are equal in magnitude but opposite in sign; that frequency is called the resonant frequency $f_O$ for the given circuit.

Hence, at resonance:

$X_L=X_C$

So the voltage across rthe unknown inductor is $200V$ as same as the voltage across the capacitor.