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A astronmical telescope has objective an...

A astronmical telescope has objective and eyepiece of focal lengths 40 cm and 4 cm respectively To view an object 200 cm away from the objective ,the lenses must be separated by a distance:

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As the object distance 10 km is much larger thanthe focal lkength 200 cm, the first imae is formed amost at the focuis of the objective. It is thus 200 cm from the objective. This image acts as the object for the eyepiece. To ge the fiN/Al image at infinity, this first image sould be at the first focus of the eyepiece.The length of the tube is therefore 200 cm+4cm=204 cm. The angular magnification in this case
`m=-f_0/f_e=200/4=-50`.
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