Question

A real image of a distant object is formed by a plano-convex lens on its principal axis. Spherical aberration is
A. Is absent
B. Is smaller if the curved surface of the lens faces the object
C. Is smaller if the plane surface of the lens faces the object
D. Is the same whichever of the lens faces the object.

Answer 1

Hint: A plano-convex lens is one in which there remains a plane-surface and a spherical surface. Students can use the idea that the focal length of a plano-convex lens is positive and also that spherical aberration occurs due to the geometry of a lens.


Complete step by step solution:
In order to answer the above question, let us first of all understand what a plano-convex lens is and what is meant by the term ‘spherical aberration’.

Definition:
Plano-convex lens: A plano-convex lens is the lens in which one of the surfaces is spherical and the other surface is plane. A lens is an optical device which focuses or disperses a light beam by means of refraction.
After this, let us know what is meant by spherical aberration. Spherical aberration is a type of aberration occurring in the optical devices which are made from materials spherical in shape. The term spherical aberration refers to a condition in which there is a loss in the definition of the image formed by a lens, which may arise due to the geometry of the lens.
This condition of aberration can be minimised by placing the curved surface facing towards the object because in that case the total deviation will be shared by both the lenses.

So, the answer is option B. is smaller if the curved surface of the lens faces the object.


Note:
The spherical aberration occurs in the lens because they have curved surfaces. We obtain a blurred image due to the spherical aberration. The light rays passing through the lens do not focus at the same point leading to a blurry image.