Question

Wavelength of radiations used in electron microscope is

• A. Less than visible light.
• B. More than visible light.
• C. Equal to visible light.
• D. Like the X-rays.

Answer 1

The correct option is A Less than visible light.

Resolving power is the ability to distinguish two close objects as distinct. It is calculated by the formula 0.61$\lambda$/ numerical aperture, where $\lambda$ is the wavelength of light and numerical aperture is the light collecting ability of lens. Actually after calculations, the value comes out to be 0.5$\lambda$ or one half the wavelength of illuminating light. The average wavelength of light used in microscopes is 500 - 600 nm. It gives a maximum resolution of 250 - 300 nm or 0.25 micrometer to 0.3 micrometer. Because the wavelength of a stream of electrons is very less, hence, the resolving power of an electron microscope is 2 to 10$\mathring{A}$. Compared with that the resolving power of an unaided human eye is 100 micrometer or 0.1 mm.