Chapter 30, Problem 4A

There are three convenient rays commonly used in ray diagrams to estimate the position of an image. Describe these three rays in terms of their orientation with respect to the principal axis and focal points.

To determine

To describe: The three convenient rays used in ray diagrams in terms of their orientation with respect to principal axis and focal points.

Explanation of Solution

Introduction:

A ray diagram is a schematic representation to draw the path of light rays which shows how they are incident and how they emerge. Its main aim is to let us identify the exact position of the image formed, its size, type of image formed and other characteristics of the image.

We have the following three convenient rays to draw a ray diagram:

• A ray parallel to principal axis: Such a ray which is incident parallel to the principal axis, passes through the focal point of lens whether it is concave or convex.
• A ray incident along the focus: Such a ray which is incident on the focal point of a lens, passes parallel to the principal axis in both the lenses.
• A ray incident along the optical centre: Such a ray which is incident along the optical centre, passes undeviated and is straight after refraction from the lens.

Conclusion:

Hence, a ray incident along principal axis, is refracted along the focus while the reverse happens if it is incident along the focus of the lens.