Question

Rays from the sun converge at a point 25 cm behind a convex lens. The distance at which an object be placed in front of the lens to get a virtual image, is:

• A. 20 cm
• B. 40 cm
• C. 50 cm
• D. More than 50 cm

Hint:

Convex lens gives virtual image only when object is within focal length.

Answer 1

The Correct Option is A

Concept: Parallel rays from the sun focus at the focal point of a convex lens. So focal length, $f = 25$ cm. Key Rule: A convex lens forms a virtual image only when the object is placed within the focal length (i.e., object distance <focal length). Analysis of Options:

• 20 cm <25 cm → Virtual image possible ✔
• 40 cm, 50 cm, more than 50 cm → Object beyond focal length → Real image ✖

Conclusion: The object must be placed closer than the focal length, so 20 cm is correct.