Question

The focal lengths of the objective and the eye-piece of a compound microscope are 2.0 cm and 3.0 cm respectively. The distance between the objective and the eye-piece is 15.0 cm. The final image formed by the eye-piece is at infinity. The two lenses are thin. The distances in cm of the object and the image produced by the objective measured from the objective lens are respectively

• A. 2.4 and 12.0
• B. 2.4 and 15.0
• C. 2.3 and 12.0
• D. 2.3 and 3.0

Answer 1

The correct option is A 2.4 and 12.0

When final image is formed at infinity
length of the tube $=v_o+f_o$
$\Rightarrow 15=v_o+3\Rightarrow v_o=12cm$
For objective lens $\frac{1}{f_o}=\frac{1}{v_o}-\frac{1}{u_o}$
$\Rightarrow \frac{1}{(+2)}=\frac{1}{(+12)}-\frac{1}{u_o}\Rightarrow u_o=-2.4cm$