Question

Assertion `:` Spherical aberration occur in lenses of larger aperture.
Reason `:` The two rays, paraxial and marginal rays focus at different points.
A. If both assertion and reason are true and reason is the correct explanation of assertion.
B. If both assertion and reason are true but reason is not the correct explanation of assertion.
C. If assertion is true but reason is false.
D. If assertion and reason both are false.

Answer 1

Correct Answer - A
In wide beam of light, the light rays of light which travel close to the principal axis are called paraxial rays, while the rays which travel quite away from the principal axis is called marginal rays. In case of lens having large aperture, the behaviour of the paraxial and marginal rays are markedly different from each other. The two types of rays come to focus at different points on the principal axis of the lens, thus the spherical aberration occur. However in cae of a lens with small aperture, the two types of rays come to focus quite close to each other.