Question

Briefly explain the principle and working of electron microscope.

Answer 1

Principle of electron microscope:

1. This is the direct application of the wave nature of particles. The wave nature of the electron is used in the construction of a microscope called an electron microscope.

2. The resolving power of a microscope is inversely proportional to the wavelength of the radiation used for illuminating the object under study. Higher magnification, as well as higher resolving power, can be obtained by employing the waves of shorter wavelengths.

3. De Broglie's wavelength of an electron is very much less than (a few thousand less) that of the visible light being used in optical microscopes.

4. As a result, the microscopes employing de Broglie waves of electrons have very much higher resolving power than the optical microscopes.

5. Electron microscopes giving magnification more than 2,00,000 times are common in research laboratories.

          (a) Optical microscope (b) Electron microscope

Working:

1. The electron beam passing across suitably arranged either electric or magnetic fields undergoes divergence or convergence thereby focussing on the beam is done.
2. The electrons emitted from the source are accelerated by high potentials. The beam is made parallel by a magnetic condenser lens. When the beam passes through the sample whose magnified image is needed, the beam carries the image of the sample.
3. With the help of a magnetic objective lens and magnetic projector lens system, the magnified image is obtained on the screen. These electron microscopes are being used in almost all branches of science.