Which physical quantity is there in $A.C.$ circuit as displacement variable?

If maximum energy is stored in the capacitor at $t = 0$,find the time after which the current in the circuit will be maximum. Given $L = 25 \, mH$ and $C = 10 \, \mu F$.

In the given circuit, the resonant frequency is (in $ Hz$)

Give the name of the physical quantity in an $LCR$ circuit that corresponds to the spring constant $k$ in forced oscillations.

$A$ capacitor of capacity $20 \mu F$ is charged to a potential of $35 \text{ V}$. The battery is then disconnected. $A$ pure inductor coil of $200 \text{ mH}$ is connected across the capacitor so that $LC$ oscillations are set up. The maximum current in the coil is: (in $\text{ A}$)

In the given circuit,when $S_1$ is closed,the capacitor gets fully charged. Now $S_1$ is opened and $S_2$ is closed. Then