BRAINCAKEElectron Microscopes
The smallest detail a microscope can show, its resolution, is limited by diffraction. Details much smaller than the wavelength of the waves used cannot be resolved, because the waves diffract around them and the images of neighbouring points blur together.
Visible light has wavelengths of about 400 nm to 700 nm, so an optical microscope cannot resolve detail finer than roughly 200 nm. Individual atoms, about 10-10 m across, are far too small to see.
An electron microscope uses a beam of electrons instead of light. The electrons are accelerated through a large potential difference, often tens of kilovolts, so they have a large momentum and a de Broglie wavelength much shorter than that of light. This gives a far better resolution.
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Key terms in this lesson
- de broglie wavelength
- The wavelength associated with a moving particle, equal to the Planck constant divided by its momentum.
More in Quantum Physics
- The Equation for the Photoelectric Effect
- Stopping Potential
- Electron Diffraction
- DeBroglie Wavelength
- Electron Energy Levels
- Excitation and De-excitation
- Line Spectra
- Exam Question 1
All 21 lessons in Quantum Physics · All Edexcel AS-level Physics topics