In an $LCR$ circuit,the resonance frequency of the circuit increases to two times its initial value by changing the capacitance from $C$ to $C^{\prime}$ and the resistance from $100 \ \Omega$ to $400 \ \Omega$,while the inductance $L$ is kept constant. The ratio $C / C^{\prime}$ is:

The plot given below is of the average power delivered to an $LRC$ circuit versus frequency. The quality factor of the circuit is

An inductor coil is connected to a capacitor and an $AC$ source of rms voltage $8 \, V$ in series. The rms current in the circuit is $16 \, A$ and is in phase with the emf. If this inductor coil is connected to a $6 \, V$ $DC$ battery, the magnitude of the steady current is (in $A$)

Figure $(a)$ shows the plot of voltage across the capacitor as a function of the driving frequency for a sinusoidally driven electromagnetic $LCR$ oscillator circuit. Figure $(b)$ shows the phase angle $\phi$ (phase difference between voltage and current) vs $\omega/\omega_0$ graph for the same circuit,for three different quality factors corresponding to graphs $1, 2, 3$ of figure $(a)$. Each graph in figure $(a)$ can be matched by one of the graphs $a, b, c$ in figure $(b)$. Choose the correct statement:

At resonance frequency,the impedance in a series $LCR$ circuit is

For a given series $LCR$ circuit,it is found that maximum current is drawn when the value of the variable capacitance is $2.5 \ nF$. If a resistance of $200 \ \Omega$ and a $100 \ mH$ inductor are being used in the given circuit,the frequency of the $AC$ source is $... \times 10^3 \ Hz$. (Given $\pi^2 = 10$)