Question

The resolution limit of eye is 1 minute. At a distance of r from the eye, two persons stand with a lateral separation of 3 metre. For the two persons to be just resolved by the naked eye, r should be

• A. 10 km
• B. 15 km
• C. 20 km
• D. 30 km
  

Answer 1

The correct option is A 10 km

From figure $\theta =\frac{d}{r}$; where $\theta =1^{\prime }={\left(\frac{1}{60}\right)}^{\circ }=\left(\frac{1}{60}\right)\times \frac{\pi }{180}rad$
$\Rightarrow 1\times \frac{1}{60}\times \frac{\pi }{180}=\frac{3}{r}\Rightarrow r=10km$