A telescope has an objective lens of 10 $\mathrm{cm}$ diameter and is situated at a distance of one…
- $0.5 \mathrm{~m}$
- $5 \mathrm{~m}$
- $5 \mathrm{~mm}$
- $5 \mathrm{~cm}$
Solution

$\begin{array}{ll}
\theta =\frac{1.22}{a} \lambda \\
\therefore \frac{d}{D} =\frac{\lambda}{\mathrm{a}} \\
\Rightarrow a^{\prime}=\frac{\lambda D}{a} \\
a =\frac{5000 \times 10^{-10} \times 10^3}{10 \times 10^{-2}}=5 \mathrm{~mm}
\end{array}$
Asked in: NEET 2004