In the circuits $(a)$ and $(b)$,switches $S_1$ and $S_2$ are closed at $t = 0$ and are kept closed for a long time. The variations of current in the two circuits for $t \ge 0$ are roughly shown by which figure? (Figures are schematic and not drawn to scale.)

Given $L_1 = 1\, mH, R_1 = 1\,\Omega, L_2 = 2\,mH, R_2 = 2\,\Omega$. Neglecting mutual inductance,find the time constant (in $ms$) for the circuit shown.

An inductor coil stores $64 \, J$ of magnetic field energy and dissipates energy at the rate of $640 \, W$ when a current of $8 \, A$ is passed through it. If this coil is joined across an ideal battery,find the time constant of the circuit in seconds.

The ratio of the time constant in charging and discharging in the circuit shown in the figure is

An inductor with an iron core is connected in series with a resistor $R$ across an ideal $DC$ source. The circuit is in a steady state. If the iron core is removed, what happens to the current flowing through the inductor immediately after the removal of the core?

An inductor of inductance $10 \text{ mH}$ having resistance of $100 \ \Omega$ is connected to a battery of $E$.$M$.$F$. $1.0 \text{ V}$ through a switch as shown in the figure below. After the switch is closed, the ratio of instantaneous voltages across the inductor when the current passing through it is $2 \text{ mA}$ and $4 \text{ mA}$ is . . . . . . .