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2.5.10 Lenses
Lens is a transparent substance with curved sides for dispersing or concentrating
light rays. The common terms with respect to lenses are given in Table 2.8.
2.5.10.1 Simple Convex Lens
A simple convex lens with parallel light rays falling on the surface is shown in
Fig. 2.17.
Suppose a lens has focal length f and an object is placed at distance s 1 from the
lens, then the image will be formed only when the equation given below is satisfied:
Fig. 2.16 Line diagram of
light passing
through a prism
Table 2.8 Definition of common terms with respect to lens
Sl.
no. Term
Description
1.
Convex lens
Lenses that are thinner at edges and thicker at the middle; rays of light
that pass through the lens converge
2.
Concave lens
Lenses that are thicker at edges and thinner at the middle; rays of light
that pass through the lens diverge
3.
Optical center of
lens
Central point of the lens through which a ray of light passes without
suffering any deviation
4.
Focal point lens Point in space where parallel light rays meet after passing through the
lens
5.
Focal length lens Distance between the focal point of lens and its optical center
6.
Optical axis of
lens/principal
axis
Straight line passing through the geometrical center of a lens and two
centers of curvature
7.
Real image
A real image is formed in the plane of convergence of rays of light that
originate from an object; real image will generally become visible on a
screen placed in the plane of a real image
8.
Virtual image
The virtual image appears to be formed when light rays that originate
from the object diverge but cannot be projected onto a screen
2.5 Optics