Explain the Principle of Microscopy?

When the light passes from one medium to another, refraction occurs, i.e., the ray is bent at the interface. The direction and the magnitude of bending are determined by the refractive indices of the two media forming the interface. The refractive index is a measure of how greatly a substance slows the velocity of light when light passes from air to glass or vice versa. When the light rays strike the lens, a convex lens will focus these rays at specific point called focal point. The distance between the center of the lens and the focal point is called the focal length. Convex lens act as a magnifier.

It provides a clear magnifying image at a much closer range. Lens strength is related to focal length. A lens with a short focal length has a more magnification power than a lens having a longer focal length. Magnification means enlargement. In compound microscope, it is carried out by two-lens system - objective lens and ocular lens. Objective lens produces the real image of the specimen, which is projected up into focal plane and then magnified by the ocular lens to produce the final image. Though magnification is important, it has limits. Unlimited enlargement by increasing magnifying power of the lenses is not possible because of the limitations of resolving power. Microscope should not only produce the enlarged image but also the clear image. Resolution or resolving power of the lens is its ability to separate two close points as separate entities.