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🔬 Comparison: Compound Microscope vs SEM vs TEM
Radiation Source
Light Microscope: Visible Light
SEM: Electron Beam
TEM: Electron Beam
Wavelength
Light Microscope: 400–700 nm
SEM/TEM: ~0.005 nm
Resolution Limit
Light Microscope: ~200 nm
SEM: ~1–10 nm
TEM: ~0.1–0.2 nm
Magnification
Light Microscope: 40x – 2000x
SEM: Up to 500,000x
TEM: Up to 2,000,000x
Image Type
Light: 2D, color
SEM: 3D, grayscale
TEM: 2D, grayscale
Formula
Electron λ: $$\lambda = \frac{h}{\sqrt{2meV}} \approx 0.0037\, \text{nm}$$
Resolution Capability
Light: ❌ Limited by diffraction
SEM: ✅ Great for surface detail
TEM: ✅ Best for internal ultrastructure
Examples in Biology
Light: Cells, tissues, bacteria (basic)
SEM: Flagella, cilia, membrane texture
TEM: Ribosomes, viruses, mitochondria
🧠 Why Electron Microscopes Have Better Resolution
Resolution $\propto$ Wavelength
Electrons have much shorter wavelengths than visible light.
Electron λ at 100 kV: $$\lambda = \frac{h}{\sqrt{2meV}} \approx 0.0037 \text{ nm}$$
Light wavelength ≈ 500 nm → limited to ~200 nm resolution
🔍 Structure Visibility
Bacteria Shape
✅ Light
✅ SEM
✅ TEM
Mitochondria
✅ Basic (Light)
❌ SEM
✅ Cristae (TEM)
Ribosomes
❌ Light
❌ SEM
✅ TEM
Flagella
❌ Light
✅ SEM
❌ TEM
🔬 Resolution vs Resolving Power
Definitions
Resolution: Minimum distance between two points that can be distinguished (lower is better).
Resolving Power: Ability to distinguish two points — it is the inverse of resolution (higher is better).
Formulas:
Resolution $\propto$ Wavelength
Resolving Power $\propto \frac{1}{\text{Wavelength}}$
Resolution $\propto$ Wavelength
Resolving Power $\propto \frac{1}{\text{Wavelength}}$