How do lenses form images?

Lenses form images by refracting light rays to converge at a focal point.

When light rays pass through a lens, they are refracted or bent due to the change in the speed of light as it passes from one medium to another. The amount of refraction depends on the shape of the lens and the angle at which the light rays enter it. A convex lens, also known as a converging lens, is thicker in the middle than at the edges. It refracts light rays inwards, causing them to converge at a focal point on the other side of the lens. The distance between the lens and the focal point is known as the focal length.

Conversely, a concave lens, also known as a diverging lens, is thinner in the middle than at the edges. It refracts light rays outwards, causing them to diverge. The focal point of a concave lens is virtual, meaning that it appears to be behind the lens. The distance between the lens and the virtual focal point is also known as the focal length.

The image formed by a lens depends on the position of the object relative to the lens and the distance between the lens and the image. When an object is placed beyond the focal point of a convex lens, a real, inverted image is formed on the opposite side of the lens. When an object is placed within the focal length of a convex lens, a virtual, upright image is formed on the same side of the lens. A concave lens always forms a virtual, upright image, regardless of the position of the object.