1. Why does an electron microscope give higher magnifications than an optical microscope?
A. Because the electrons have more energy than light particles
B. Because the velocity of electrons is less than that of light
C. Because the wavelength of electrons used is smaller compared to that of visible light
D. Because the electron microscope uses more powerful lenses
Correct Answer: C. Because the wavelength of electrons used is smaller compared to that of visible light
Electron microscopes achieve higher magnification because electrons have de Broglie wavelengths (~0.005 nm at 100 kV) thousands of times smaller than visible light (~400-700 nm), enabling sub-nanometer resolution vs optical limits of ~200 nm.
Option Analysis
A. Because the electrons have more energy than light particles
Incorrect. Energy affects penetration depth, not resolution. Resolution is governed by wavelength (λ), where d = 0.61λ/NA. Photon energy (visible light: ~2 eV) vs electron kinetic energy (~100 keV) is irrelevant to diffraction limit.
B. Because the velocity of electrons is less than that of light
Incorrect. Electrons in EMs accelerate to ~0.5c (50% light speed). Slower velocity would increase wavelength (λ = h/mv), reducing resolution—opposite of reality.
C. Because the wavelength of electrons used is smaller compared to that of visible light (Correct)
Resolution limit: d = 0.61λ/NA. Visible light λ = 550 nm → d ≈ 200 nm. Electrons at 100 kV: λ ≈ 0.0037 nm → d ≈ 0.1 nm. Smaller λ enables atomic-scale imaging.
D. Because the electron microscope uses more powerful lenses
Incorrect. EM uses electromagnetic lenses with similar NA (~0.01) to glass lenses. Resolution gain comes from λ, not lens power. Aberrations limit EM lenses more than glass optics.
Electron microscope gives higher magnifications than optical microscope because electron wavelength is smaller than visible light—fundamental wave-particle duality principle for GATE Life Sciences.
Resolution Formula
Resolution (d) = 0.61 × λ / NA
λlight = 550 nm → d ≈ 200 nm
λelectron (100 kV) = 0.0037 nm → d ≈ 0.1 nm
Microscope Comparison
| Feature | Optical Microscope | Electron Microscope |
|---|---|---|
| Wavelength | 400-700 nm | 0.001-0.005 nm |
| Max Magnification | 1,500× | 1,000,000× |
| Resolution | 200 nm | 0.1 nm |
| Sample Prep | Live cells OK | Fixed, vacuum |
GATE Applications
Tests de Broglie hypothesis (λ = h/p), microscopy principles in biophysics. TEM/SEM distinguish viruses (20-300 nm), ribosomes (25 nm) invisible to light microscopy.
