Optics 5 Question 1

1. The value of numerical aperture 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

(2019 Main, 12 April I)

(a) 0.24μm

(b) 0.38μm

(c) 0.12μm

(d) 0.48μm

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Answer:

Correct Answer: 1. (a)

Solution:

  1. Key Idea

Numerical Aperture (NA) of the microscope is given by NA=0.61λd

Here, d= minimum separation between two points to be seen as distinct and λ =wavelength of light.

Given, λ=5000\AA=5000×1010m and NA=1.25

Now, d=0.61λNA=0.61×5000×10101.25

ord=3.051.25×107m=2.4×107mord=0.24μm



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