|
Spherical lenses: Curvature of Optical Precision:
|
- A transparent material bound by two surfaces, of which one or both surfaces are spherical, forms a lens.
- This means that a lens is bound by at least one spherical surface.
- In such lenses, the other surface would be plane.
|
|
Double Convex Lens: Optical Prowess through Dual Spherical Surfaces:
|
- A lens may have two spherical surfaces, bulging outwards.
- Such a lens is called a double convex lens.
- It is simply called a convex lens.
- It is thicker at the middle as compared to the edges.
|
|
Converging Lenses : Optical Power in Convex Marvels:
|
- Convex lenses converge light rays.
- Hence convex lenses are also called converging lenses.
|
|
Diverging Lenses: Optical Expansion through Concave Marvels:
|
- A double concave lens is bounded by two spherical surfaces, curved inwards. It is thicker at the edges than at the middle.
- Such lenses diverge light rays.
- Such lenses are also called diverging lenses.
- A double concave lens is simply called a concave lens.
|
|
Spherical surfaces
|
- A lens, either a convex lens or a concave lens, has two spherical surfaces.
- Each of these surfaces forms a part of a sphere.
|
|
Centre of Curvature in Lenses:
|
- Focal Heart of Optical Precision: The centres of these spheres are called centres of curvature of the lens.
- The centre of curvature of a lens is usually represented by the letter C.
- Since there are two centres of curvature, we may represent them as C1 and C2.
|
|
Principal Axis in Lenses: Mapping the Optical Axis of Precision:
|
- An imaginary straight line passing through the two centres of curvature of a lens is called its principal axis.
- The central point of a lens is its optical centre.
- It is usually represented by the letter O.
- A ray of light through the optical centre of a lens passes without suffering any deviation.
|
|
Aperture in Spherical Lens:
|
- The effective diameter of the circular outline of a spherical lens is called its aperture.
|
|
Principal Focus on Concave Lens: Convergence of Light Rays:
|
- Several rays of light parallel to the principal axis are falling on a convex lens.
- These rays, after refraction from the lens, are converging to a point on the principal axis.
- This point on the principal axis is called the principal focus of the lens.
|
|
Principal Focus on Concave Lens: Divergence of Light Rays:
|
- Several rays of light parallel to the principal axis are falling on a concave lens.
- These rays, after refraction from the lens, are appearing to diverge from a point on the principal axis.
- This point on the principal axis is called the principal focus of the concave lens.
 (a) Converging action of a convex lens, (b) diverging action of a concave lens
- If parallel rays pass from the opposite surface of the lens, another principal focus on the opposite side is made.
- Letter F is usually used to represent principal focus.
- However, a lens has two principal foci.
- They are represented by F1 and F2 .
- The distance of the principal focus from the optical centre of a lens is called its focal length.
- The letter f is used to represent the focal length.
|