The Simple Microscope The simple microscope is an instrument used for viewing close objects with a single optical system. This is popularly known as a magnifying or reading glass.

Construction and Working It consists of a single positive (converging) lens which is used close against the eye. The function of the lens is to allow the eye to focus on an object nearer than the least distance of comfortable (distinct) vision. A simple microscope in which L is a lens and MI is the least distance of comfortable vision. An eye E cannot see clearly an object O without the aid of the lens L. For clear vision, the maximum angle is subtended at the eye by the object when it is placed at I. If the object is brought nearer to the eye, the subtended angle alfa would be larger, but the image would not be clear because MI is the least distance for distinct vision. But, with the aid of the lens L, the image of the object OP is formed at IR and both the object and the image subtend the same angle at the eye placed close to the lens. Thus, the image appears both distinct and magnified.

Magnification of the Simple Microscope The magnification of a simple microscope is the ratio of the least distance of distinct vision to the focal length of the lens. If the focal length of the lens is f.

Limitations In a simple microscope, the lesser the focal length the greater is the magnification. However, since the curvature of the surface increases with increase in focal length of the lens, if is not possible to obtain a lens of very small focal length. As a result a large magnification cannot be obtained from a simple microscope.