Final answer:
Concave curves on a lens clock are read as negative values, reflecting the fact that concave lenses are diverging lenses with a negative focal length, causing parallel rays to spread apart.
Step-by-step explanation:
On a lens clock, which is used to measure the curvature of lenses, concave curves are read as negative values. A lens clock works by comparing the curvature of the lens to a known curvature, and the readings indicate whether the lens surface is concave (diverging) or convex (converging). Concave lenses, also known as diverging lenses, cause light rays that enter them parallel to their optical axis to spread out or diverge. This is because the shape of a concave lens is thinner in the middle and thicker at the edges. The focal length of a concave lens is defined to be negative, indicating that the light rays appear to originate from a point behind the lens if extended backward. The lens clock reading gives a negative value for the curvature of a concave lens, which aligns with how its focal length is represented.
The focal length and path of the light rays through a diverging lens are key concepts in understanding how a lens affects light. For example, the focal length of a lens determines where light rays converge or appear to originate from after passing through the lens. In the case of a concave lens, light rays that enter parallel to the lens axis diverge, and when traced back, they seem to come from a common point known as the focal point.