Basics of a Microscope - Engineering Physics

A microscope is a device which is used to view the magnified image of a smaller object, which cannot be clearly seen through a naked eye.

In general, we can classify the microscope as simple and compound microscope. A simple microscope is made of a single biconvex magnifying lens held in a simple frame. A compound microscope is made of two lenses (or) system of lenses for better magnification. These types of microscopes give a stereoscope vision and also reduce the strain of our eyes.

Magnifying power

The magnifying power

(M)

of a microscope is defined as the ratio between the angle subtended by the final image at the eye

(β)

to the angle subtended by the object at the eye

(α)

, placed at the nearest point.

$M=\frac{\text { Angle substended by the final image at eye }}{\text { Angle subtended by the object at eye placed at a near point }}$

$M=\frac{\beta}{\alpha}$

Resolving power

It is the ability of an optical instrument to form distinct and separable images of the two point objects which are close to each other.

If ‘ d’ is the distance between two close point objects, then we can write

$\mathrm{d}=\frac{\lambda_{0}}{2 \mathrm{NA}}$

$\therefore \text { Resolving power }=\frac{1}{\mathrm{~d}}=\frac{2 \mathrm{NA}}{\lambda_{0}}$

Where NA – Numerical Aperture of the objective of the microscope and

$λ 0$ – Wavelength of light through vacuum.

Therefore, the resolving power of a microscope can be increased by decreasing the value of $λ 0$ . Thus, by using ultraviolet light and quartz lenses, the resolving power can be increased.