Q27. An astronomical telescope has fₒ = 80 cm, fₑ = 5 cm and normal-adjustment separation 85 cm. The two lenses are interchanged but kept 85 cm apart. Viewed from the new objective, the angular magnification magnitude becomes:
Options

Question

Q27. An astronomical telescope has fₒ = 80 cm, fₑ = 5 cm and normal-adjustment separation 85 cm. The two lenses are interchanged but kept 85 cm apart. Viewed from the new objective, the angular magnification magnitude becomes:

Options

G1 Physics · Accepted Answer

GIVEN: Initial objective focal length 80 cm, eyepiece 5 cm; normal-adjustment separation L = 85 cm. Step 1: Interchange lenses: new objective fₒ' = 5 cm, new eyepiece fₑ' = 80 cm. Step 2: Normal-adjustment length after interchange remains fₒ' + fₑ' = 5 + 80 = 85 cm, so the given separation still works. Step 3: New angular magnification magnitude |M'| = fₒ'/fₑ' = 5/80 = 1/16 = 0.0625. Step 4: Telescope now reduces apparent angular size instead of magnifying it. FINAL ANSWER: 1/16. Option C.