Question

Cardinal points of the system of coaxial lenses are

A. Set of focal points
B. Set of principal points
C. Both (A) and (B)
D. None of these

Answer 1

Hint: The lens system which have a common optical axis is known as Co-axial lens system. It consists number of lenses placed apart with a common optical axis known as Principal axis. An optical system consists of six cardinal points which are two focal point, two nodal point and two principal points. These points are used to approximate the behavior of real optical systems.

Complete answer:
For any given system of lenses, there are few points known as Cardinal points. These points help to determine the image formation in a lens system without knowing the structure of the system. These cardinal points lie on the optical axis of the optical system of lenses. It consists of three pairs i.e. six points located on the optical axis of the rotationally symmetric, focal and optical system. These three pairs of points are namely focal points, nodal points and the principal points. So, there are two nodal points, two focal points and two principal points.
Thus, Cardinal points of the system of coaxial lenses are focal points and principal points.

So, the correct answer is option C i.e. both A and B.

Note:
The basic imaging properties such as size and location of an image can be determined with the help of the locations of the cardinal points. Students must remember to do this only four points are necessary: two focal points and either two principle points or two nodal points. The only ideal system that the physicists have actually achieved is a plane mirror.