Resolution power of light microscope is
Resolution power, or resolving power, of a light microscope refers to its ability to distinguish between two closely spaced objects. The formula for resolution is often given by the Rayleigh criterion: d = 0.61 * λ / (n * sinθ), where λ is the wavelength of light, n is the refractive index of the medium, and θ is the half-angle of the maximum cone of light entering the lens.
The typical resolution limit for a light microscope is around 0.2 micrometers (200 nanometers) when using visible light. This is because the wavelength of visible light ranges from about 400 to 700 nm, and the maximum numerical aperture (n*sinθ) of a high-quality lens is around 1.4. Plugging these into the formula gives a resolution near 0.2 micrometers. Electron microscopes have much higher resolution because they use electrons with much shorter wavelengths.
Now, considering standard options for this question, common distractors might include lower values like 0.1 micrometers (which is actually the theoretical limit for electron microscopes), or higher values like 1 micrometer. The correct answer should be 0.2 micrometers. Let me check if there's any other possible correct answer. For example, some sources might mention 0.2 micrometers as the resolving power, while others might use 200 nm. Since micrometers and nanometers are both used, I need to confirm the units in the options. If the options are in micrometers, 0.2 is correct. If in nanometers, 200 nm.
So, the correct answer is likely 0.2 micrometers or 200 nm. The clinical pearl here is that the resolving power of a light microscope is limited by the wavelength of light, which is why electron microscopes (using shorter wavelengths) achieve much higher resolution.
**Core Concept**
Resolution power (or resolving power) of a light microscope is the minimum distance between two points that can be distinguished as separate. It is governed by the wavelength of light and the numerical aperture of the lens. The theoretical limit is approximately 0.2 micrometers (200 nm) for visible light.
**Why the Correct Answer is Right**
The resolving power of a light microscope is calculated using the Rayleigh criterion: $ d = frac{0.61 lambda}{n sin theta} $, where $ lambda $ is the wavelength of light (~400–700 nm for visible light), $ n $ is the refractive index of the medium (e.g., air = 1.0, oil = 1.5), and $ theta $ is the half-angle of the lens aperture. For typical visible light and high-quality lenses, this yields a resolution limit of ~0.2 micrometers (200 nm). This is why structures smaller than this, like ribosomes or most viruses,