Q. The graph shows how the magnification $m$ produced by a convex thin lens varies with image distance $v$. What was the focal length of the used lines
A) $b/c$
B) $b/ca$
C) $bc/a$
D) $c/b$
Explanation
(d) For a lens $m = \frac{f - v}{f} = - \frac{1}{f}v + 1$
Comparing it with $y = mx + c$
Slope $= m = - \frac{1}{f}$
From graph, slope of the line $= \frac{b}{c}$
Hence $- \frac{1}{f} = \frac{b}{c} \Rightarrow |f| = \frac{c}{b}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.