Question

The focal lengths of the objective and the eyepiece of an astronomical telescope are 20 cm and 5 cm respectively. If the final image is formed at a distance of 30 cm from the eyepiece, find the separation between the lenses required for distinct vision

• A. 32.4 cm
• B. 42.3 cm
• C. 24.3 cm
• D. 30.24 cm

Answer 1

The correct option is C 24.3 cm

$f_0=20cm$

$f_e=5cm$

$V_e=30cm=D$

$L=?$

$L_D=f_0+\frac{D{f}_e}{D+f_e}$ $=20+\frac{5\times 30}{35}=24.3cm$