2018 · Q28
When a convex lens produces a real image of an object, the minimum distance between the object and image is equal to
General KnowledgePhysics
- Athe focal length of the convex lens
- Btwice the focal length of the convex lens
- Cfour times the focal length of the convex lens
- Done half of the focal length of the convex lens
Explanation
When a convex lens forms a real image, the object-image separation is minimised when the object is at 2F, producing an image of equal size at 2F on the other side. The minimum separation is then 2f + 2f = 4f. It cannot be smaller than four times the focal length for any real image. Hence the minimum distance equals four times the focal length.