Question

Electron microscope has a high resolution power. This is due to

• A. Electromagnetic lenses
• B. Very low wavelength of electron beam
• C. Low wavelength of light source used
• D. High numerical aperture of glass lenses used.

Answer 1

The Correct Option is B

In order to understand why the electron microscope has a high resolution power, we must delve into the basic principles of how electron microscopes function compared to traditional optical microscopes.

Resolution in microscopy refers to the ability to distinguish two separate points as distinct entities. The resolution power of a microscope is influenced by the wavelength of the light or wave used for illumination. According to the formula for resolving power:

d = \frac{\lambda}{2 \cdot NA}

• \lambda: Wavelength of the light/electron beam
• NA: Numerical Aperture of the lens system

From the formula, it is clear that a smaller wavelength leads to a smaller value of d, which means higher resolution.

Let's consider the options given:

• Electromagnetic lenses: Although electromagnetic lenses are used to focus electron beams, they do not directly contribute to high resolution by themselves.
• Very low wavelength of electron beam: This is the correct answer. Electrons, when accelerated, have a much shorter wavelength than visible light, significantly improving resolution.
• Low wavelength of light source used: Electron microscopes do not use light; they use electron beams, which have much shorter wavelengths.
• High numerical aperture of glass lenses used: Numerical aperture is important, but glass lenses are not used in electron microscopes. Instead, electromagnetic lenses are used due to the electron beam's nature.

In conclusion, the primary reason for the high resolution power of an electron microscope is the very low wavelength of the electron beam, allowing it to differentiate between points that are much closer together compared to optical microscopes using visible light.