The Optics of Lenses Science Words Convex Lenses convex lens

    Do you wear glasses or contact lenses? If so, you use lenses to improve concave lens

    your ability to see. Like curved mirrors, lenses are described as convex or

    concave, depending on their shape.

    Convex lenses are thicker in the middle than at the edges. Light rays Objectives

    approaching the lens parallel to the optical axis are refracted toward the • Describe the types of images

    formed with convex and center of the lens. They converge at the focal point, so they are capable of concave lenses. forming real images that can be projected onto a screen. • Cite examples of how these The amount of refraction depends on the change in the speed of light as it lenses are used. passes through a material and the shape of the object. As shown in Figure • Explain how lenses are used 20-6, thick lenses with highly curved surfaces bend light much more than to correct vision.

    thin ones with less curved surfaces. The focal length of the thick convex lens

    in the top diagram in Figure 20-6 is shorter than that of the thin convex lens Figure 20-6 below it. Convex lenses can produce many kinds of images, both real and A thick convex lens (A) bends virtual, upright, inverted, enlarged, or reduced. The type of image formed light more than a thin convex depends on the position of the object and the focal length of the lens. The lens (B). Which lens has the diagrams in Figure 20-7 show the images that result from three different shorter focal length?

    locations of the object and focal point.

    The image formed by a convex lens depends upon the location of the object relative to the focal length of the lens.A. If a person is photographing a faraway object, it's

    likely that the object is more than two focal lengths

    from the camera lens. If you follow the light paths,

    you'll notice that the real image is smaller than the

    object, and inverted. The lens in your eye forms

    images in the same way that a camera forms images B. If an object is between one and two focal lengths from

    the lens, the real image is inverted and larger than the

    object. This is the method used to project a movie from

    a small film to the large screen of a theater or from an

    overhead projector to a screen in your classroom. C. Have you ever used a magnifying glass to closely

    examine an object? A magnifying glass is a convex

    lens, so you must hold it less than one focal length

    from the object. The light rays can't converge, and an

    enlarged, upright, and virtual image is formed. Look at

    the position of the image. Notice that the object seems

    larger and farther away than it really is.

Concave Lenses

    Concave lenses are thinner in the middle and thicker at the edges. As is shown in Figure 20-8, light passing

    through a concave lens bends toward the edges. The Figure 20-8

    rays diverge and never form. a real image. The image Light rays passing through a is virtual, upright, and smaller than the actual object. concave lens diverge and The image formed by a concave lens is similar to the form a virtual image. Are

    concave lenses similar to or image produced by a convex mirror because they both

    different from convex mirrors? diverge light to form virtual images.Concave lenses are usually used in combination with other lenses. They can be used with convex lenses in telescopes and cameras to spread out incoming light and extend the focal length so you can see a clear image of a faraway object. Concave lenses are also used to correct nearsighted vision.