Chapter 30, Problem 5A

To determine

To state: The minimum number of rays required to form an image.

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.

Out of these three rays, we require at least two rays to form image formation by a lens. At least two lines are required to show the intersection between them so if we draw a minimum of two rays from an object, it is easy for us to locate the position and nature of the image by looking at their intersection points.

Conclusion:

Hence, we need at least two rays to show image formation in a lens.