Q. The focal lengths of the objective and eyelenses of a microscope are 1.6 cm and 2.5 cm respectively. The distance between the two lenses is 21.7 cm. If the final image is formed at infinity, the distance between the object and the objective lens is
A) 1.8 cm
B) 1.70 cm
C) 1.65 cm
D) 1.75 cm
Explanation
(d) $L = v_{0} + f_{e} \Rightarrow v_{0} = L - f_{e}$
Or ${\ v}_{0} = 19.2\ cm$
$\frac{1}{19.2} - \frac{1}{u_{0}} = \frac{1}{1.6}$
Or $- \frac{1}{u_{o}} = \frac{10}{16} - \frac{10}{192}$
Or $- \frac{1}{u_{o}} = \frac{120 - 10}{192} = \frac{100}{192}$
Or ${\ u}_{o} = - \frac{192}{110}\ $cm$\ = - 1.75\ $cm
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.