What is a lens?

A lens is defined as a thin, transparent piece of glass or plastic that has at least one curved surface. This curvature allows the lens to bend light rays that pass through it, which can focus or disperse the light in various ways to form images.

Lenses play a crucial role in many optical devices, such as glasses, cameras, and microscopes, by manipulating light in a controlled manner. The curved surfaces of the lens create different focal lengths depending on the shape and material, leading to various applications in vision correction and image formation.

The other choices do not accurately represent a lens. For example, while a piece of glass that absorbs light might exist, it does not serve the essential function of bending light like a lens does. Additionally, a thick piece of optically dark material does not have the properties necessary to focus or transmit light effectively. Lastly, a device that amplifies sound waves is unrelated to optics, as it pertains to acoustics rather than the manipulation of light.