Topic outline
- Types of lenses
- Terms used in thin lenses
- Locating images by ray diagrams
- Characteristics of images formed by thin lenses
- Magnification formula
- Lens formula
- Experiments to determine the focal length of a convex lens
- The human eye
- Optical devices
- Project work: Construction of a compound microscope
Types of lenses
Converging (convex) lenses and diverging (concave) lenses
There are mainly two types of lenses namely convex (converging) lens and concave (diverging) lens.
A convex lens is thicker at its centre than at its edges. It converges light rays incident on it. A bi-convex or double convex lens has both its surfaces ‘curving out’. Other convex lenses are plano-convex and concavo-convex or converging meniscus (Fig. 1.1).
Bi-convex or double convex
Plano - convex
Concavo - convex (Converging miniscus)
Fig. 1.1: Types of convex lenses
A concave lens is thicker at its edges than at its centre and diverges the light rays incident on it. A bi-concave or double concave lens has both its surfaces ‘curving in’. Other concave lenses are plano-concave and convexo-concave or diverging meniscus (Fig. 1.2).
Bi-concave or double concave
Plano-concave
Convexo-concave (diverging meniscus)
Fig. 1.2: Types of concave lenses
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