Optics 7 Question 7
7. Assuming human pupil to have a radius of $0.25 cm$ and a comfortable viewing distance of $25 cm$, the minimum separation between two objects that human eye can resolve at $500 nm$ wavelength is
(2015 Main)
(a) $30 \mu m$
(c) $100 \mu m$
(b) $1 \mu m$
(d) $300 \mu m$
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Answer:
Correct Answer: 7. (a)
Solution:
Resolving angle of naked eye is given by
$$ \begin{array}{rlrl} & \theta & =\frac{1.22 \lambda}{D} \\ \therefore \quad & \quad \frac{y}{25 \times 10^{-2}} & =\frac{1.22 \times 500 \times 10^{-9}}{0.25 \times 2 \times 10^{-2}} \\ \therefore & y & =30 \times 10^{-6} m \\ & =30 \mu m \end{array} $$
