5.57. Lens http://www.ck12.org
5.57 Lens
- Describe a lens and what it does.
- Compare and contrast concave and convex lenses.
The tiny object on this man’s finger is life-changing for him. It lets him see clearly without wearing glasses. You
probably recognize the object as a contact lens. You may even wear contact lenses yourself.
What Is a Lens?
Alensis a transparent object with one or two curved surfaces. It is typically made of glass (or clear plastic in the
case of a contact lens). A lens refracts, or bends, light and forms an image. An image is a copy of an objected
formed by the refraction (or reflection) of visible light. The more curved the surface of a lens is, the more it refracts
the light that passes through it. There are two basic types of lenses: concave and convex. The two types of lenses
have different shapes, so they bend light and form images in different ways.
Concave Lens
A concave lens is thicker at the edges than it is in the middle. You can see the shape of a concave lens in theFigure
5.131. From the diagram, it’s clear that the lens causes rays of light to diverge, or spread apart, as they pass through
it. Note that the image formed by a concave lens is on the same side of the lens as the object. It is also smaller than
the object and right-side up. However, it isn’t a real image. It is a virtual image. Your brain “tricks” you into seeing
an image there. The light rays actually pass through the glass to the other side and spread out in all directions. You
can explore the formation of images by a concave lens at this URL: http://phet.colorado.edu/sims/geometric-optics/g
eometric-optics_en.html