question_answer

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                                        [RPET 1997; RPMT 2000]

A)            3.2 m                                       

B)            20.8 m

C)            91.5 m                                     

D)            183 m

Correct Answer: A

Solution :

                   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., \[\frac{d}{x}>\left( \frac{1}{60} \right)\times \frac{\pi }{180}\]                    \[\Rightarrow d>\frac{\pi \times x}{60\times 180}\]            \[\Rightarrow d>\frac{3.14\times 11\times {{10}^{3}}}{60\times 180}\]\[\Rightarrow d>3.2\ m\]