Name ______
“Lenses and Refraction of Light” Article
Have you ever looked through binoculars, used a microscope or a camera, or worn eyeglasses? If so, you have used a lens to bend light. A lens is a curved piece of glass or other transparent material that is used to refract light. A lens forms an image by refracting light rays that pass through it. Like mirrors, lenses, can have different shapes. The type of image formed by a lens depends on the shape of the lens. Lenses are classified by their shape. Two kinds of lenses, convex and concave, are shown in the diagrams below. The center beams in each diagram show that light rays that pass through the center of any lens are not refracted. Remember that refraction only occurs when light enters a new medium at an angle.
Convex Lenses
A convex lens is a lens that is thicker in the middle than at the edges. As parallel light rays pass through a convex lens, they are bent toward the center of a lens. The rays meet at a focal point and then continue on. The more curved the lens the more it refracts light. A convex lens can focus rays of light to a single point, depending on the position of the object in relationship to the lens. As the diagram below shows, a convex lens can form an upside down (if the object is farther from the lens than from where the rays of light cross) or a right side up image (if the object is so close to the lens that the rays cannot cross).
Convex lenses have many uses. For example, magnifying lenses and camera lenses are convex lenses. And convex lenses are sometimes used in eyeglasses.
The distance between an object and a convex lens determines the size and the kind of image formed.
CONCAVE LENSES
A concave lens is thinner in the center than at the edges. As parallel rays of light pass through a concave lens, they are bent away from the center of the lens. The figure below shows how the rays spread out.
A concave lens refracts parallel rays of light so that they appear to cross in front of the lens. The rays never meet. So, concave lens, like convex mirrors, never form an upside down image.
Concave lens are sometimes combined with other lenses in telescopes. The combination of lenses produces clearer images of distant objects. Concave lenses are also used in microscopes and eyeglasses.
Lenses and Light Review
Answer the questions below in COMPLETE sentences on page 73 in your INB.
1). What is a lens?
2). How does a lens form images?
3). What determines the type of image formed by a lens?
4). How are lenses classified?
5). What happens to light rays as they pass from one medium into another medium?
6). Describe the shape of a convex lens and explain what happens to light that passes
through a convex lens.
7). What determines whether or not a convex lens can focus light on a single point?
8). Where does a convex lens needs to be positioned in relationship to an object for an
upside down image to form? A right side up image?
9). Describe the shape of a concave lens and explain what happens to light that passes
through a concave lens.
10), Why do concave lenses never form an upside down image?
THINK ABOUT IT!!!
11). . Suppose you wanted to closely examine the leaf of a plant. Which type of lens
would you use? Explain.