Question

An astronomical telescope has a converging eyepiece of focal lengths 5 cm and objective of focal lengths 80 cm. When the final image is formed at the least distance of distinct vision (25 cm), the separation between the two lenses is-

• A. 75.0 cm
• B. 80.0 cm
• C. 82.2. cm
• D. 85.0 cm

Answer 1

Answer: (C)

82.2. cm

Answer 2

l = f_o t = S_o t $\frac { 5 \times 25 } { 5 + 25 }$

= S_o t $\frac { 125 } { 30 }$= 84.16 = 84.2 cm