Two thin conducting shells of radii $R$ and $3R$ are shown in the figure. The outer shell carries a charge $+Q$ and the inner shell is neutral. The inner shell is earthed with the help of a switch $S$.

For the circuit shown in the figure,the charge on the $4 \mu F$ capacitor is $....... \mu C$.

If an electron enters into a space between the plates of a parallel plate capacitor at an angle $\alpha$ with the plates and leaves at an angle $\beta$ to the plates,the ratio of its kinetic energy while entering the capacitor to that while leaving will be

Identify the correct statements:
$A$. Effective capacitance of a series combination of capacitors is always smaller than the smallest capacitance of the capacitor in the combination.
$B$. When a dielectric medium is placed between the charged plates of a capacitor,displacement of charges cannot occur due to the insulation property of the dielectric.
$C$. Increasing the area of the capacitor plate or decreasing the thickness of the dielectric is an alternate method to increase the capacitance.
$D$. For a point charge,concentric spherical shells centered at the location of the charge are equipotential surfaces.
Choose the correct answer from the options given below.

Capacitor $A$ has a capacitance of $1\ \mu F$. It is filled with a dielectric medium of constant $K = 15$. Another capacitor $B$ has a capacitance of $1\ \mu F$. Both are charged separately by $100\ V$ batteries. After charging,the batteries are removed,the dielectric is removed from $A$,and the capacitors are connected in parallel. Calculate the common potential in $V$.

Two parallel plate capacitors with capacitances $C$ and $2C$ are connected in parallel. They are charged to a potential difference $V$. Now,if the battery is disconnected and a dielectric of dielectric constant $K$ is inserted between the plates of the capacitor with capacitance $C$,find the potential difference across each capacitor.