Explanation

(a) In Galiean telescope a convergent lens is used as the objective and a divergent lens as the eyepiece. Magnifying power and length of telescope are written as
$M = \frac{f_{0}}{u_{e}}and\ L = f_{0} - u_{e}$
In normal adjustment, ie, in relaxed eye state
$u_{e} = f_{e}$
So, $M_{\infty} = \frac{f_{0}}{f_{e}} = 50$
$or\ f_{e} = \frac{f_{0}}{50} = \frac{100}{50} = 2\ cm\ $
And $L_{\infty} = f_{0}\ –f_{e}$
$\therefore L_{\infty}$ = 100-2 = 98 cm