The value of numerical aperature of the objective lens of a microscope is 1.25. If light of wavelength $5000 \AA$ is used, the minimum separation between two points, to be seen as distinct, will be :

JEE Main · 2019 · 12 Apr 2019 · Shift 1 · Wave Optics

The value of numerical aperature of the objective lens of a microscope is 1.25. If light of wavelength

5000 \overset{˚}{A}

is used, the minimum separation between two points, to be seen as distinct, will be :

(A) $0.48 μ m$
(B) $0.38 μ m$
(C) $0.24 μ m$ ✓ Correct
(D) $0.12 μ m$

Answer: (C)

Solution

The smallest separation a microscope can resolve is

d = \frac{0.61 λ}{NA}

, where NA is the numerical aperture. Putting in

λ = 5000 \overset{˚}{A} = 5 \times 1 0^{- 7} m

and

NA = 1.25

, we get

d = \frac{0.61 \times 5 \times 1 0 ^{- 7}}{1.25} = 2.44 \times 1 0^{- 7} m \approx 0.24 μ m

JEE Main · 2019 · 12 Apr 2019 · Shift 1 · Single correct option

Practise more: all JEE Main PYQs on Wave Optics →

More JEE Main questions on Wave Optics

Given below are two statements:
Statement I: In a Young's double slit experiment, the angular separation of fringes will increase as the screen is moved away from the plane of the slits
Statement II : In a Young's double slit experiment, the angular separation of fringes will inc …
JEE Main 2026View solution →
In a Young's double slit experiment set up, the two slits are kept 0.4 mm apart and screen is placed at 1 m from slits. If a thin transparent sheet of thickness $20 μ m$ is introduced in front of one of the slits then centre bring fringe shifts by 20 mm on the screen …
JEE Main 2026View solution →
In two separate Young's double-slit experimental set-ups, two monochromatic light sources of different wavelengths are used to get fringes of equal width. The ratios of the slit separations and that of the wavelengths of light used are $2 : 1$ and $1 : 2$ respectively. The correspo …
JEE Main 2026View solution →
When an unpolarized light falls at a particular angle on a glass plate (placed in air), it is observed that the reflected beam is linearly polarized. The angle of refracted beam with respect to the normal is $____$ .
( $tan^{- 1} (1.52) = 57. 7^{\circ}$ , refractive indices of air a …
JEE Main 2026View solution →
Given below are two statements:

Statement-I: A plane wave after passing through prism remains as plane wave but passing through small pin hole may become spherical wave.
Statement-II: The curvature of a spherical wave emerging from a slit will increase for increasing slit width. …
JEE Main 2026View solution →
In the Young's double slit experiment the intensity produced by each one of the individual slits is $I_{0}$ . The distance between two slits is 2 mm. The distance of screen from slits is 10 m. The wavelength of light is $6000 \overset{˚}{A}$ . The intensity of light on the screen in front of …
JEE Main 2026View solution →