Question

The value of numerical aperture of the objective lens of a microscope is 1.25. If light of wavelength 5000A˚ is used, the minimum separation between two points, to be seen as distinct, will be :
(A) 0.24μm
(B) 0.48μm
(C) 0.12μm
(D) 0.38μm

Answer 1

Hint
There are several different types of microscopes used in light microscopy, and the four most popular types are Compound, Stereo, Digital and the Pocket or handheld microscopes. Some types are best suited for biological applications, where others are best for classroom or personal hobby use.

Complete step by step answer
According to the question, numerical aperture of the microscope is,
$NA = \dfrac{{0.61\lambda }}{d}$
According to the formula where $\lambda$ = wavelength and d = minimum separation between two points to be seen as distinct.
$\Rightarrow d = \dfrac{{0.61\lambda }}{{NA}}$
Now, putting the values from given question,we get,
∴ $d = \dfrac{{(0.61) \times (5000 \times 10{m^{ - 10}})}}{{1.25}}$ … converting armstrong into meter]
$\begin{gathered} \Rightarrow d = 2.4 \times {10^{ - 7}}m \\\ \therefore d = 0.24\mu m \\\ \end{gathered}$
Option (A) is correct answer.

Note
Most microscopes fit into one of three main types - compound, stereoscopic and electron.
- Compound: The Old Standby. The most-used microscope, particularly in schools, is the compound microscope, which uses visible light to illuminate a sample.
- What to Use for Larger Objects.
- Looking at Objects in 3D.
- Notable Mention