Question

When a set of parallel rays of light inclined at 15° to the principal axis, are incident on a convex lens, they

• A. Converge at focus (F)
• B. Diverge from focus (F)
• C. Converge to a point on focal plane
• D. Diverge from a point on focal plane

Answer 1

The Correct Option is C

To solve this problem, we need to understand the behavior of parallel rays incident on a convex lens at an angle to the principal axis.

1. Behavior of Parallel Rays in Convex Lens:
In a convex lens, parallel rays that are incident along the principal axis converge at the principal focus on the opposite side.

2. Inclined Parallel Rays:
When rays are parallel but inclined (at 15° in this case) to the principal axis, they do not converge at the principal focus directly. Instead, they converge at a point on the focal plane — the plane that is perpendicular to the principal axis and passes through the focus.

3. Evaluating the Options:
(A) Converge at focus (F) – Incorrect (only rays parallel to principal axis do this)
(B) Diverge from focus (F) – Incorrect (diverging happens in concave lenses)
(C) Converge to a point on focal plane – Correct ✅
(D) Diverge from a point on focal plane – Incorrect

Final Answer:
The correct option is (C) Converge to a point on focal plane.