# DBT JRF 2022 — Question 38

Exam: DBT JRF 2022 · Section: B · Topic: Cell Biology › Microscopy & Resolution · Difficulty: Medium

## Question

A conventional light microscope allows us to magnify cells up to 1000 times and to resolve details as small as ______________.

## Options

- **A.** 200 µm
- **B.** 200 nm
- **C.** 0.2 nm
- **D.** 20 nm

## Answer

Option B

## Explanation

Resolution limit of a light microscope: The resolution limit of a light microscope is governed by the Abbe diffraction limit: $d = \frac{\lambda}{2 \cdot n \sin\theta} = \frac{\lambda}{2\,\text{NA}}$ where $\lambda$ = wavelength of light, NA = numerical aperture. For visible light ( $\lambda \approx 400-700\,\text{nm}$ ) with best NA: $d \approx \frac{550\,\text{nm}}{2 \times 1.4} \approx 200\,\text{nm} = 0.2\,\mu\text{m}$ Comparison: • Light microscope: resolution ~200 nm (cannot resolve structures smaller than ~0.2 µm) • Transmission Electron Microscope (TEM): resolution ~0.1–1 nm (can resolve individual atoms) • Scanning Electron Microscope (SEM): resolution ~1–10 nm Answer: ~200 nm (0.2 µm) resolution limit for light microscopy.

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