Question

A convex lens form image of an object at infinity. Object is at

• A. focus (F)
• B. C = 2 f
• C. infinity
• D. pole (P)

Answer 1

The Correct Option is A

To solve this problem, we need to determine the object position when a convex lens forms an image at infinity.

1. Image at Infinity by Convex Lens:
A convex lens forms an image at infinity when the object is placed at the lens’s focus (F).

2. Behavior of Light Rays:
When parallel rays (like those from a distant object) pass through a convex lens, they converge at the focus. Conversely, if the object is at the focus, the refracted rays go parallel to the principal axis, appearing to meet at infinity—hence, the image forms at infinity.

3. Evaluating the Options:

• (A) Focus (F) – Correct ✔
• (B) \( C = 2f \) – Incorrect; this forms an image at the same distance on the other side.
• (C) Infinity – Incorrect; object at infinity forms image at focus.
• (D) Pole (P) – Incorrect; not relevant to lenses, more to mirrors.

Final Answer:
The correct answer is (A) Focus (F).