4. A microscope can distinguish two closely situated points and the distance between those points is known as the ______ of the microscope.
Correct Answer
C. Resolving power. This measures the minimum resolvable distance (typically ~0.2 μm for light microscopes), calculated as d = 0.61λ/NA where λ is wavelength and NA is numerical aperture.
Option Breakdown
- A. Magnification: Incorrect. Magnification enlarges the image size (e.g., 1000×) but doesn’t improve detail separation; empty magnification occurs beyond resolving limits.
- B. Illumination: Incorrect. Illumination provides light intensity/quality (e.g., Köhler) but doesn’t determine point separation ability.
- C. Resolving power: Correct. Ernst Abbe defined it as the shortest distance
dbetween points whose images are distinct; higher resolving power = smallerd. - D. Focal length: Incorrect. Focal length is a lens property affecting working distance/magnification, not resolution of close points.
Microscope Resolving Power Explained
Microscope resolving power determines the smallest distance between two points that appear distinct, crucial for cell biology imaging in life sciences.
Abbe’s equation RP = 2NA/λ shows resolution improves with shorter wavelengths (blue light > red) and higher numerical aperture (oil immersion > air). Typical light microscope limit: 200 nm.
Key Differences Table
| Term | Definition | Formula/Example | GATE Relevance |
|---|---|---|---|
| Resolving Power | Min separable distance | d = 0.61λ/NA ~0.2 μm | Q4 direct test |
| Magnification | Image enlargement | 40×, 100× objective | Empty beyond RP |
| Illumination | Light source quality | Halogen, LED | Contrast aid only |
| Focal Length | Lens focus distance | 10 mm objective | Mechanical |
Oil immersion (NA=1.4) achieves ~0.15 μm vs air (NA=0.95) ~0.22 μm.
Exam Strategy
GATE tests Abbe criterion: remember resolving power = 1/distance. Electron microscopes (~0.5 nm) vastly exceed light microscopes.
