Q45. An astronomical telescope initially has fₒ = 100 cm and fₑ = 10 cm. Its objective focal length increases by 20%, while eyepiece focal length decreases by 20%. In normal adjustment the new tube length and angular magnification magnitude are:
Options

Question

Q45. An astronomical telescope initially has fₒ = 100 cm and fₑ = 10 cm. Its objective focal length increases by 20%, while eyepiece focal length decreases by 20%. In normal adjustment the new tube length and angular magnification magnitude are:

Options

G1 Physics · Accepted Answer

GIVEN: Original telescope fₒ = 100 cm and fₑ = 10 cm. Objective focal length increases by 20%; eyepiece focal length decreases by 20%. Step 1: New objective focal length fₒ' = 100 × (1 + 20/100) = 120 cm. Step 2: New eyepiece focal length fₑ' = 10 × (1 − 20/100) = 8 cm. Step 3: Normal adjustment length L' = fₒ' + fₑ' = 120 + 8 = 128 cm. Step 4: New angular magnification magnitude |M'| = fₒ'/fₑ' = 120/8 = 15. FINAL ANSWER: 128 cm and 15. Option B.