Which of the following devices allows light to focus, creating a real image?

• A. Flat mirror
• B. Convex lens
• C. Opaque card
• D. Concave lens

Answer: (B)

The correct answer, which is the convex lens, effectively focuses light to create a real image. A convex lens is thicker in the middle than at the edges, which allows it to bend and converge light rays that travel through it. When parallel rays of light enter a convex lens, they are refracted and meet at a focal point on the opposite side of the lens. If an object is placed outside this focal point, the light rays from the object converge and create a real image that can be projected onto a screen.

In contrast, a flat mirror merely reflects light without focusing or converging those rays, so it can generate a virtual image that appears behind the mirror but not a real one that can be projected. An opaque card blocks light entirely and does not allow any light to pass through or focus, eliminating the possibility of image formation. A concave lens, on the other hand, diverges light rays and only produces virtual images that cannot be projected onto a surface. Thus, the unique ability of the convex lens to converge light rays is what makes it the device that creates real images.