Ray Optics and Optical Instruments - Result Question 70
74. A telescope has an objective lens of $10 cm$ diameter and is situated at a distance of one kilometer from two objects. The minimum distance between these two objects, which can be resolved by the telescope, when the mean wavelength of light is $5000 \AA$, is of the order of
(a) $5 cm$
(b) $0.5 m$
(c) $5 m$
(d) $5 mm$
[2004]
Show Answer
Answer:
Correct Answer: 74. (d)
Solution:
(d) Here, $\frac{x}{1000}=\frac{1.22 \lambda}{D}$
or, $x=\frac{1.22 \times 5 \times 10^{3} \times 10^{-10} \times 10^{3}}{10 \times 10^{-2}}$
or, $x=1.22 \times 5 \times 10^{-3} m=6.1 mm$
$\therefore x$ is of the order of $5 mm$.
