Q. Two parallel pillars are $11\ km$ away from an observer. The minimum distance between the pillars so that they can be seen separately will be
A) $3.2\ m$
B) $20.8\ m$
C) $91.5\ m$
D) $183\ m$
Explanation
(a) As limit of resolution of eye is $\left( \frac{1}{60} \right)^{o}$, the pillars will be seen distinctly if $\theta > \left( \frac{1}{60} \right)^{o}$
$i.e.,\frac{d}{x} > \left( \frac{1}{60} \right) \times \frac{\pi}{180}$
$\Rightarrow d > \frac{\pi \times x}{60 \times 180}$
$\Rightarrow d > \frac{3.14 \times 11 \times 10^{3}}{60 \times 180} \Rightarrow d > 3.2\ m$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.