Define the following terms focal length, center of curvature, radius of curvature, principal axis?

1. Focal length: The focal length of a lens or mirror is the distance between the focal point and the optical center of the lens or mirror. It is a measure of how strongly the lens or mirror converges or diverges light.

2. Center of curvature: The center of curvature is the point located at a distance equal to the radius of curvature from the vertex of a curved mirror or lens. It is the center of the sphere of which the mirror or lens is a part.

3. Radius of curvature: The radius of curvature is the distance between the center of curvature and the vertex of a curved mirror or lens. It is half of the diameter of the sphere of which the mirror or lens is a part.

4. Principal axis: The principal axis is an imaginary line that passes through the center of curvature and the vertex of a curved mirror or lens. It is used as a reference line for measuring distances and angles in optical systems.

Focal Length:

- The distance between the optical center of a lens and the point where parallel rays of light converge after passing through the lens.

Center of Curvature:

- The center of the sphere from which a lens is formed.

Radius of Curvature:

- The distance between the optical center of a lens and the center of curvature.

Principal Axis:

- The straight line passing through the optical center of a lens and perpendicular to the curved surfaces of the lens.