Q23. In normal adjustment an astronomical telescope has angular magnification magnitude 40 and tube length 82 cm. Its objective and eyepiece focal lengths, respectively, are:
Options

Question

Q23. In normal adjustment an astronomical telescope has angular magnification magnitude 40 and tube length 82 cm. Its objective and eyepiece focal lengths, respectively, are:

G1 Physics · Accepted Answer

GIVEN: Normal-adjustment telescope: magnification magnitude |M| = 40, tube length L = 82 cm. Step 1: Normal adjustment relations: |M| = fₒ/fₑ = 40, and L = fₒ + fₑ = 82 cm. Step 2: From the first relation, fₒ = 40 fₑ. Step 3: Substitute: 40 fₑ + fₑ = 82 ⇒ 41 fₑ = 82. Step 4: fₑ = 82/41 = 2 cm; fₒ = 40 × 2 = 80 cm. Step 5: Verification: 80 + 2 = 82 cm, 80/2 = 40. FINAL ANSWER: Objective 80 cm, eyepiece 2 cm. Option A.