5.3 Using Lenses to Form Images A lens is a curved piece of transparent material that can bend, or refract, light rays in useful ways to help form a well-focused image. A lens can be concave or convex. See page 190 (c) McGraw Hill Ryerson 2007

are thinner in the middle than at the edge. Concave Lenses Concave lenses: are thinner in the middle than at the edge. cause light rays to diverge. See page 191 (c) McGraw Hill Ryerson 2007

produce images that are upright and smaller than the object. Concave Lenses Concave Lenses: produce images that are upright and smaller than the object. are sometimes used in eyeglasses and telescopes. (c) McGraw Hill Ryerson 2007

are thicker in the middle than at the edge. Convex Lenses Convex lenses are thicker in the middle than at the edge. cause light rays to converge. When parallel rays strike a convex lens they come together at the focal point. A magnifying glass is a good example of a convex lens. See page 192 (c) McGraw Hill Ryerson 2007

Focal length in Convex Lenses The distance from the centre of the lens to the focal point is called the focal length. The type of image a convex lens forms depends on where the object is relative to the focal point. See page 193 Take the Section 5.3 Quiz (c) McGraw Hill Ryerson 2007