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Question:

Out of the five incident rays shown in the figure, find the three rays that are obeying the laws of refraction and may be used for locating the position of the image formed by a convex lens.

2, 3 and 4

1, 2 and 3

3, 4 and 5

1, 2 and 4

Solution:

The incident ray parallel to the principal axis passes through the focus of the lens after refraction and vice-versa. And the ray doesn’t deviate when it is incident on the optical center. Thus rays 2 and 4 obey the law of refraction. Also, the ray through the optical center of the lens passes undeviated, i.e., ray 3 also obeys the refraction law. Thus option B is correct.