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

Answer: (A)

10 km

Answer 2

From figure $\theta = \frac{d}{r}$; where

$\theta = 1' = \left( \frac{1}{60} \right)^{o} = \left( \frac{1}{60} \right) \times \frac{\pi}{180}rad$

⇒ $1 \times \frac{1}{60} \times \frac{\pi}{180} = \frac{3}{r}$ ⇒ r = 10 km