A simple telescope consisting of an objective of focal length 60 cm and a single eye lens of focal length 5 cm is focussed on a distant object in such a way that parallel rays emerge from the eye lens. If the object subtend an angle of 2° at the objective then find the angular width of the image (in degree).
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Question

A simple telescope consisting of an objective of focal length 60 cm and a single eye lens of focal length 5 cm is focussed on a distant object in such a way that parallel rays emerge from the eye lens. If the object subtend an angle of 2° at the objective then find the angular width of the image (in degree).

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G1 Physics · Accepted Answer

Derived solution: Step 1: For an astronomical telescope use angular magnification |M| = fₒ/fₑ and, in normal adjustment, tube length = fₒ + fₑ. Step 2: Substitute the values given in the question and apply the geometry/sign convention shown. Step 3: On simplification the result is 24. Therefore the correct option is A.