Question

Define the following terms:

(a) Principal axis of a lens

(b) Focal length of a lens

(c) Power of a lens

(d) Optical center of a lens

(e) Focal plane of a lens

Answer 1

1. The optical or principal axis is defined as a straight line that connects the center of curvatures of two curved surfaces of the lens.

1. The distance between the optical center and the focus of a lens is called the focal length of the lens.
2. The power of a lens is inverse of its focal length measured in meters.
3. The optical center of a lens is the center point of the lens.
4. The focal plane of a lens is an imaginary plane that is at right angles to the principal axis and passes through the focus of a lens.