Explanation

(a) Power of lens, $P$ (in dioptre) $= \frac{100}{focal\ length\ f\ (in\ cm)}$
$\therefore f = \frac{100}{10} = 10\ cm$
According to lens maker’s formula
$\frac{1}{f} = (\mu - 1)\left( \frac{1}{R_{1}} - \frac{1}{R_{2}} \right)$
For biconvex lens $R_{1} = + R,\ R_{2} = - R$
$\therefore\frac{1}{f} = (\mu - 1)\left( \frac{1}{R} + \frac{1}{R} \right)$
$\Rightarrow \frac{1}{f} = (\mu - 1)\left( \frac{2}{R} \right)$
$\frac{1}{10} = (\mu - 1)\left( \frac{2}{10} \right)$
$\Rightarrow (\mu - 1) = \frac{1}{2}$
$\mu = \frac{1}{2} + 1 = \frac{3}{2}$