In the given circuit, the box $B$ either contains a capacitor, or an inductor or a resistor. The current $I$ versus time $t$ plots for three cases $\left(a_1, a_2, a_3\right)$ are shown in figures. The switch $S$ is closed at time $t=0$. Which of the following is correct?

In the given circuit each of the resistors is of $1 \mathrm{k} \Omega$ resistance and each of the capacitors has $4 \mu \mathrm{~F}$ capacitance. What is the charge in the capacitor between the points B and F ?

A thin lens made of material of refractive index $n_l$ forms the image at the position $I$ of a point object held at $O$ on the central axis of the lens, as is shown in the ray diagram below. Consider that the refractive index of the medium is $n_m$ and $n_l>n_m$ for the figure given. Where does the image form when $n_l

A conducting sphere of radius $a$ initially contains a uniform volume charge density $\rho$. What is the electric flux $\Phi$ through a spherical surface of radius $2 a$ centered at a point on the surface of the charged sphere (see figure) at a later time $t$ ? ( $\epsilon_0$ is the permittivity of free space.)