Question

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

Answer 1

Answer: (A)

3.2 m

Answer 2

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., $\frac { d } { x } > \left( \frac { 1 } { 60 } \right) \times \frac { \pi } { 180 }$

$\Rightarrow d > \frac { \pi \times x } { 60 \times 180 }$

$\Rightarrow d > \frac { 3.14 \times 11 \times 10 ^ { 3 } } { 60 \times 180 }$