Understanding Concave Lens Properties

A concave lens is a diverging lens. When parallel light rays pass through it, they diverge (spread out).

Image Formation by Concave Lenses

• When a real object is placed in front of a concave lens, the lens always forms a virtual, upright, and diminished image.
• This virtual image is formed on the same side of the lens as the object and cannot be projected onto a screen.
• Real images, which can be formed on a screen, are typically formed by converging lenses (like convex lenses) when the object is placed beyond the focal point.

Identifying the Mistake

The student's observation that a concave lens formed a diminished real image on the screen contradicts the fundamental properties of a concave lens with a real object.

• A concave lens diverges light and produces virtual images, not real images that can be captured on a screen.
• Therefore, the mistake is the assertion that a concave lens can form a real image under these conditions.

The error is: Concave lens cannot form a real image (from a real object, which is the standard assumption in such problems).