Q21. An astronomical telescope has fₒ = 100 cm and fₑ = 5 cm. In normal adjustment, the angular magnification magnitude and tube length are respectively:
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Question

Q21. An astronomical telescope has fₒ = 100 cm and fₑ = 5 cm. In normal adjustment, the angular magnification magnitude and tube length are respectively:

G1 Physics · Accepted Answer

GIVEN: Astronomical telescope fₒ = 100 cm, fₑ = 5 cm; both lenses converging; normal adjustment. Step 1: Distant object forms the intermediate image at the objective focus, vₒ = fₒ = 100 cm. Step 2: To get parallel emerging rays, intermediate image must lie at the eyepiece front focus, 5 cm to its left. Step 3: Tube length L = fₒ + fₑ = 100 + 5 = 105 cm. Step 4: Angular magnification magnitude |M| = fₒ/fₑ = 100/5 = 20. FINAL ANSWER: Magnification 20; length 105 cm. Option A.