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  4. A small telescope has an objective lens of focal length 140 cm and an eyepiece of focal length 5.0 cm. The magnifying power of the telescope for viewing distant objects when the final image is formed at the least distance of distinct vision 25 cm is

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Q. A small telescope has an objective lens of focal length $140\, cm$ and an eyepiece of focal length $5.0 \,cm$. The magnifying power of the telescope for viewing distant objects when the final image is formed at the least distance of distinct vision $25\, cm$ is

Ray Optics and Optical Instruments

Solution:

When the final image is formed at least distance of distinct vision $d$, magnifying power of the telescope is
$m =\frac{f_{0}}{f_{e}}\left(1+\frac{f_{e}}{d}\right) $
$= \frac{140}{5}\left(1+\frac{5}{25}\right) = 33.6$