The GATE Grind

GATE 2025 MT – Question 17

Physical Metallurgy · Materials characterization · 1 mark · Multiple choice

In optical microscopy, which one of the following combinations of wavelength (λ) and numerical aperture (NA) provides the best spatial resolution?

  1. $\lambda=400\ \mathrm{nm},\ NA=1.0$
  2. $\lambda=600\ \mathrm{nm},\ NA=1.2$
  3. $\lambda=400\ \mathrm{nm},\ NA=1.2$
  4. $\lambda=600\ \mathrm{nm},\ NA=1.0$

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Show answer and explanation

Correct answer: (C) $\lambda=400\ \mathrm{nm},\ NA=1.2$

Explanation

The minimum resolvable spacing scales as λ/NA. Comparing the choices, the shortest wavelength, 400 nm, combined with the largest numerical aperture, 1.2, minimizes that ratio. Thus **C** gives the best resolution; a larger resolvable spacing would mean poorer resolution.