Explain the following as applicable to:

Lens
Optical Centre
Principal Focus
Focal length

In the context of lenses in Physics, here are the definitions for the terms you asked about:

Lens : A lens is a transparent optical element with two surfaces that refract light. Lenses can be made from glass or plastic and come in various shapes. They are used in many devices such as glasses, cameras, and microscopes.

Optical Centre : The optical centre of a lens is a point on the principal axis of the lens where a ray of light passes through without changing its direction. In other words, light passing through the optical centre of a lens does not bend and continues in a straight line.

Principal Focus : The principal focus (or focal point) of a lens is a point on the principal axis where light rays that are parallel to the principal axis either converge (in the case of a converging lens, like a convex lens) or appear to diverge from (in the case of a diverging lens, like a concave lens) after passing through the lens.

Focal Length : The focal length of a lens is the distance from the optical centre of the lens to the principal focus. It is usually denoted by the letter f . The focal length determines the converging or diverging power of the lens. Shorter focal lengths lead to stronger converging or diverging effects.


Understanding these terms is crucial for studying the properties of lenses and how they manipulate light to form images.

Answered by danjohnbrain | 2025-07-06