Rules for obtaining images formed by spherical lens

Following are the rules which are used for obtaining the images formed by spherical lenses.

1. A ray of light from the object parallel to the principal axis of a lens passes through the principal focus (of a convex lens) or appears to pass through the principal focus (of a concave lens) after refraction.
2. A ray of light passing through the optical centre of a lens goes straight without any deviation after refraction.
3. A ray of light passing through the principal focus (of a convex lens) or appearing to pass through the principal focus (of a concave lens) emerges parallel to the principal axis after refraction.

Test Your Understanding and Answer These Questions:

1. What are the rules for obtaining images formed by spherical lenses?