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Question:

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

0.12µm

0.38µm

0.24µm

0.48µm

Solution:

The correct option is A
0.24µm
Numerical aperture of the microscope is given as
NA = 0.61λ/d
Where d = minimum separation between two points to be seen as distinct
d = 0.61λ/NA = (0.61) × (5000 × 10⁻⁷m)/1.25 = 2.4 × 10⁻⁷m = 0.24µm