Q. An object is viewed through a compound microscope and appears in focus when it is 5 mm away from the objective lens. When a sheet of transparent material 3 mm thick is placed between the objective and the microscope, the objective lens has to be moved 1 mm to bring the object back into the focus. The refractive index of the transparent material is
A) $1.5$
B) $1.6$
C) $1.8$
D) $2.0$
Explanation
(a) Shift$\ = t\left( 1 - \frac{1}{\mu} \right)$
$1 = 3\left( 1 - \frac{1}{\mu} \right)or\ \ \frac{1}{3} = 1 - \frac{1}{\mu}$
Or $\frac{1}{\mu} = 1 - \frac{1}{3} = \frac{2}{3}\ or\ \mu = \frac{3}{2} = 1.5$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.