Image Formation by Convex and Concave Lenses: Rules of Refraction

Images Formed Due to Refraction Through a Convex and Concave Lens

When an object is placed in front of a lens, the light rays from the object fall on the lens. The position, size and nature of the image formed can be understood only if we know certain basic rules.

Rule 1:

When a ray of light strikes the convex or concave lens obliquely at its optical centre, it continues to follow its path without any deviation (Figure 2.3).

Figure 2.3 Rays passing through the optical centre of convex and concave lenses

Rule 2:

When rays parallel to the principal axis strikes a convex or concave lens, the refracted rays are converged to (convex lens) or appear to diverge from (concave lens) the principal focus (Figure 2.4).

Figure 2.4 Rays passing parallel to the optic axis for convex and concave lenses

Rule 3:

When a ray passing through (convex lens) or directed towards (concave lens) the principal focus strikes a convex or concave lens, the refracted ray will be parallel to the principal axis (Figure 2.5).

Figure 2.5 Rays passing through or directed towards the principal focus for convex and concave lenses

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10th Science : Chapter 2 : Optics : Images Formed Due to Refraction Through a Convex and Concave Lens