5.3 Using Lenses to Form Images A lens is a curved piece of transparent material that can bend (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

Light rays refract through glass in predictable ways. Not in your notes Light rays refract through glass in predictable ways. Recall when light passes from air to a denser material like glass, it bends toward the normal. When it passes out of the glass, it bends away from the normal. (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 (spread out) and never meet. No focal point. Curve inward See page 191 (c) McGraw Hill Ryerson 2007

Image is always upright and smaller than the object. Concave Lenses Image is always upright and smaller than the object. (c) McGraw Hill Ryerson 2007

Concave Lenses - Uses Sometimes used in eyeglasses( for nearsightedness) and contacts, flashlights, peepholes, binoculars, telescopes, and in photography. (c) McGraw Hill Ryerson 2007

Convex lenses are thicker in the middle. cause light rays to converge (come together) at a focal point. See page 192 (c) McGraw Hill Ryerson 2007

A light ray passing straight through the center is not refracted Convex Lenses Light passing through the thicker, more curved areas will bend more than light passing through flatter areas. A light ray passing straight through the center is not refracted See page 192 (c) McGraw Hill Ryerson 2007

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

Image depends on how far the object is from the focal point. Convex Lenses Image depends on how far the object is from the focal point. The distance from the centre of the lens to the focal point is called the focal length. (c) McGraw Hill Ryerson 2007

Focal Length When object is more than two focal lengths away from the lens, its image is reduced and upside down (c) McGraw Hill Ryerson 2007

Convex Lens and Focal Length When object is between one and two focal lengths from the lens, its image is enlarged and upside down. (c) McGraw Hill Ryerson 2007

Convex Lens and Focal Length When object is at one focal length from the lens, there is no image because rays never meet. (c) McGraw Hill Ryerson 2007

Convex Lens and Focal Length When object is less than one focal length from the lens, its image is enlarged and upright. (c) McGraw Hill Ryerson 2007

(c) McGraw Hill Ryerson 2007

Convex Lens Microscopes, magnifying glass Camera lens (c) McGraw Hill Ryerson 2007

Focal length in Convex Lenses If an object is between the lens and the focal point (less than on focal length), the image is upright and larger than the object. If an object is more than one focal length away form the lens, the image is upside down and smaller than the object. See page 193 Take the Section 5.3 Quiz (c) McGraw Hill Ryerson 2007

(c) McGraw Hill Ryerson 2007

Homework Read pages190-193 Answer (c) McGraw Hill Ryerson 2007