
This potential difference is divided among two capacitors $\mathrm{C}_{1}$ and $\mathrm{C}_{2}$ in the inverse ratio of their capacities (as they are joined in series).
$\therefore $ $\mathrm{V}_{1}=\frac{\mathrm{C}_{2}}{\mathrm{C}_{1}+\mathrm{C}_{2}} \mathrm{V}=\frac{4}{2+4} \times 12=8 \mathrm{\,volt}$
As plate of capacitor $\mathrm{C}_{1}$ towards point $\mathrm{B}$ will be at $+$ $\mathrm{ve}$ potential, hence
${{\rm{V}}_{\rm{B}}} - {{\rm{V}}_{\rm{A}}} = 8{\mkern 1mu} \,{\rm{volt}}$ or
$\mathrm{V}_{\mathrm{A}}-\mathrm{V}_{\mathrm{B}}=-8 \mathrm{\,V}$
| Capacitor | Capacitance |
| $(A)$ Cylindrical capacitor | $(i)$ ${4\pi { \in _0}R}$ |
| $(B)$ Spherical capacitor | $(ii)$ $\frac{{KA{ \in _0}}}{d}$ |
| $(C)$ Parallel plate capacitor having dielectric between its plates | $(iii)$ $\frac{{2\pi{ \in _0}\ell }}{{ln\left( {{r_2}/{r_1}} \right)}}$ |
| $(D)$ Isolated spherical conductor | $(iv)$ $\frac{{4\pi { \in _0}{r_1}{r_2}}}{{{r_2} - {r_1}}}$ |


$\left(\frac{1}{4 \pi \in_{0}}=9 \times 10^{9} Nm ^{2} / C ^{2}\right)$
$\left(\frac{1}{4 \pi \epsilon_{0}}=9 \times 10^{9} Nm ^{2} / C ^{2}\right)$
