Parallel rays of light incident on a concave lens are refracted in such a way that they appear to diverge from a point on the principal axis. This virtual point is also called the principal focus, but in this case, it represents the point from which the rays seem to be coming.
How does the behavior of parallel rays of light differ when passing through a concave lens?
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When parallel rays of light pass through a concave lens, they diverge as if coming from a point on the same side of the lens from which they originated. Unlike convex lenses, concave lenses are diverging lenses, causing the rays to spread out. This apparent divergence occurs due to the lens’s ability to refract light away from its optical axis. The point from which the divergent rays appear to originate is called the virtual focal point. Concave lenses are commonly used in corrective eyeglasses for individuals with nearsightedness, as they help to diverge incoming light rays before entering the eye, allowing proper focus on the retina.