Question

The basic principle behind the working of an electron microscope is:

• A. Using charged mirrors to achieve the desired magnification.
• B. Magnifying power of very thin aperture convex lenses.
• C. Electrostatic field created by a beam of electrons.
• D. Wave nature of electrons.

Hint:

To get high resolution, you need very small wavelengths. Since electrons act as waves with extremely short de Broglie wavelengths when accelerated, they can resolve atomic-scale details that regular light waves simply blur over!

Answer 1

The Correct Option is D

Concept: According to the de Broglie hypothesis, moving material particles like electrons exhibit a dual wave-particle character. The equivalent matter wavelength is given by $\lambda = \frac{h}{p}$. Because electrons can be accelerated to high velocities using electric potentials, their associated wavelengths can be made thousands of times smaller than the wavelength of visible light.

Step 1: Relate matter waves to resolution properties.
The resolving limit of any imaging system is fundamentally restricted by the wavelength of the illumination source used (diffraction limit). Standard optical microscopes cannot resolve structures smaller than the wavelength of visible light ($\approx 4000 - 7000\text{ }^\circ\text{A}$). By using accelerated electron beams instead of light waves, an electron microscope achieves wavelengths on the order of fractions of an Angstrom. This massive reduction in wavelength provides a significantly higher resolving power, making the wave nature of electrons the operational foundation of the device.