How do concave lenses affect light rays?

Concave lenses cause light rays to diverge, spreading them outwards as they pass through the lens.

When light rays enter a concave lens, which is thinner in the middle and thicker at the edges, they are refracted or bent outwards. This bending occurs because of the change in speed as light moves from one medium (air) into another (glass or plastic of the lens). The shape of the concave lens causes the light rays to spread apart, or diverge, rather than coming together at a point.

Imagine parallel light rays entering a concave lens. As they pass through, each ray is bent away from the central axis of the lens. If you trace these diverging rays backward, they appear to come from a single point called the focal point, which is located on the same side of the lens as the incoming light. This focal point is virtual because the light rays do not actually meet there; it is just where they seem to originate from.

Concave lenses are often used in devices like glasses for people who are short-sighted (myopic). In short-sightedness, the eye's lens focuses images in front of the retina rather than directly on it. A concave lens helps by diverging the light rays before they enter the eye, moving the focal point back onto the retina and allowing for clear vision.

In summary, concave lenses are essential in various optical applications because they spread light rays apart, helping to correct vision problems and manipulate light paths in scientific instruments. Understanding how they work is a fundamental part of GCSE Physics, as it helps explain broader concepts of light behaviour and optics.