Question

In a compound microscope, the focal lengths of two lenses are 1.5 cm and 6.25 cm an object is placed at 2 cm form objective and the final image is formed at 25 cm from eye lens. The distance between the two lenses is

• A. 6.00 cm
• B. 7.75 cm
• C. 9.25 cm
• D. 11.00 cm

Answer 1

The correct option is D 11.00 cm

It is given that $f_0=1.5cm,f_e=6.25cm,u_0=2cm$
When final image is formed at least distance of distinct vision, length of the tube $L_D=\frac{u_0{f}_0}{u_0-f_0}+\frac{f_{e}D}{f_e+D}$
$\Rightarrow L_D=\frac{2\times 1.5}{2-1.5}+\frac{6.25\times 25}{6.25+25}=11cm.$