An astronomical telescope of ten-fold angular magnification has a length of 44 cm. The focal length of the objective is:
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Question

An astronomical telescope of ten-fold angular magnification has a length of 44 cm. The focal length of the objective is:

G1 Physics · Accepted Answer

Step 1: In normal adjustment, M = fₒ/fₑ = 10. Step 2: Telescope length L = fₒ + fₑ = 44 cm. Step 3: Put fₒ = 10fₑ ⇒ 11fₑ = 44 ⇒ fₑ = 4 cm. Step 4: fₒ = 10 × 4 = 40 cm. Final answer: (C) 40 cm.