
$\frac{15 \times 30}{25}=3 \times 6$ or $V_{A}-V_{a}=18$ ...........$(1)$
also
$ \mathrm{V}_{\mathrm{A}}-\mathrm{V}_{\mathrm{b}} =\frac{\mathrm{C}_{4}}{\mathrm{C}_{3}+\mathrm{C}_{4}} \times 30 $
$=\frac{0.5}{2.5+0.5} \times 30$
$\mathrm{V}_{\mathrm{A}}-\mathrm{V}_{\mathrm{b}}=\frac{0.5}{2.5+0.5} \times 10=5 \mathrm{V}$ .........$(2)$
equation $(1)$ and $ \mathrm{Eq}.$ $(2)$
$\mathrm{V}_{\mathrm{b}}-\mathrm{V}_{\mathrm{a}}=18-5=13 \mathrm{\,volt}$


