Q.
A thin plano-convex lens of focal $f$ is split into two halves. One of the halves is shifted along the optical axis. The separation between object and image plane is 1.8 m. The magnification of the image formed by one of the half lens is 2. Find the focal-length of the lens and separation between the two halves
A) 0.1 m
B) 0.4 m
C) 0.9 m
D) 1 m
Explanation
(b) This is a modified displacement method problem
Here,$\ a = 1.8$m and $\ \frac{a + d}{a - d} = \frac{2}{1}$
Solving we get $d = 0.6\ $m
$\therefore f = \frac{a^{2} - d^{2}}{4a}$
$= 0.4$m
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.