- Draw the ray diagram of an astronomical telescope when the final image is formed at infinity. Write the expression for the resolving power of the telescope.
- An astronomical telescope has an objective lens of focal length 20m and eyepiece of focal length 1cm.
- Find the angular magnification of the telescope.
- If this telescope is used to view the Moon, find the diameter of the image formed by the objective lens. Given the diameter of the Moon is $3.5 \times 10^6m$ and radius of lunar orbit is $3.8 \times 10^8m.$
CBSE 55-1-1 PAPER SET 2020
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Resolving power $=\frac{\text{D}}{1.22\lambda}$
- $\text{m}=-\frac{\text{f}_0}{\text{f}_\text{e}}=-\frac{20}{10-2}=-2000$
$\tan\alpha=\frac{\text{d}_0}{\text{u}}=\frac{\text{di}}{\text{f}_0}$
$\Rightarrow\text{d}_1=\frac{3.5\times10^6}{3.8\times10^8}\times20=0.18\text{m}$
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