Question

A point object is held above a thin equiconvex lens at its focus. The focal length is $0.1m$ and the lens rests on a horizontal thin plane mirror. The final image will be formed at :

• A. Infinite distance above the lens
• B. $0.1m$ above the center of the lens
• C. Infinite distance below the lens
• D. $0.1m$ below the center of the lens

Answer 1

Answer: (B)

$0.1m$ above the center of the lens

Since the object is placed at focus, first, the ray will pass through the lens and incident normally on the plane mirror. Now the ray which has fallen on the plane mirror, will reflected back to focus through the lens. Because the rays fell on the mirror are parallel. Hence the two rays will meet at focus of the lens which results in formation of image of the object at focus only. So, the image will form at a distance of $0.1m$ above the center of the lens. Hence option B is correct.