When a parallel plate capacitor is charged up to 95 V , its capacitance is $C$. If a dielectrtic slab of thickness 2 mm is inserted between plates and distance between the plates is increased by 1.6 mm such that the same potential difference is maintained. The dielectric constant of the material (slab) is

The capacitance of an isolated sphere of radius $r_1$ is increased by 5 times, when it is enclosed by an earthed concentric sphere of radius $r_2$. The ratio of their radii is

Two figures are shown as Fig. $A$ and Fig. $B$. The time constant of Fig. $A$ is $\tau_A$ and time constant of Fig. $B$ is $\tau_B$. Then

Three parallel plate capacitors of capacitances $4 \mu \mathrm{~F}$, $6 \mu \mathrm{~F}$ and $12 \mu \mathrm{~F}$ are first connected in series and then in parallel. The ratio of the effective capacitances in the two cases is