What are Spherical Lenses ?
- Lenses are defined as transparent materials which are bounded by two surfaces, out of which one or both can be spherical.
- When both the two spherical surfaces bulge outwards, it is known as convex lens. They converge the light rays.
- When the two spherical surfaces bulge inwards, they are known as concave lens. They are known as diverging lens.
|
Convex Lens |
Concave Lens |
| Thin from corners | Thick from corners |
| Thick at center | Thin at centre |
| Converging | Diverging |
Important terms related to Spherical Lenses
Pole (P): The midpoint or the symmetric centre of a Spherical lens is known as its Optical Centre. It is also called as the Pole.
Principal Axis: The imaginary straight line passing through the Optical Centre and the Centre of Curvature.
Paraxial Ray: A ray close to Principal Axis and also parallel to it.
Centre of curvature (C): The centres of the spheres that the spherical lens was a part of. A spherical lens has two Centre of Curvature..
Focus (F): It is the point on the axis of a lens to which parallel rays of light converge or from which they appear to diverge after refraction.
Focal length: Distance between Optical Centre and Focus.
Concave lens: Diverging lens
Convex lens: Converging lens
Rules for Image Formation by Convex lens and Concave lens
Ray Diagram of Images Formed using Convex Lens
Ray Diagram of Images Formed using Concave Lens
Uses of Spherical Lens
Spherical Lenses are used in Visual Aids such as in Spectacles, Binoculars, Magnifying Lens, Telescopes.