LECTURE 17 MIRRORS AND THIN LENS EQUATION Instructor: Kazumi Tolich Lecture 17 2 ¨ 18.6 Image formation with spherical mirrors ¤ Concave mirrors ¤ Convex mirrors ¨ 18.7 The thin-lens equation ¤ Sign conventions for lenses and mirrors 18.6 Image formation with spherical mirrors ¨ Spherical mirrors (concave mirrors and convex mirrors) can be used to form images. Quiz: 18.6-1 4 18.6 Concave mirrors ¨ The special rays for a concave mirror: 18.6 Concave mirrors ¨ For the ray trace, incoming rays are drawn as if they are reflect off the mirror plane, not off the curved surface of the mirror. ¨ The image is real if rays converge at the image point. 18.6 Convex mirrors ¨ The special rays for a convex mirror: 18.6 Convex mirrors ¨ Diverging rays appear to diverge from the virtual image. 18.7 The thin-lens equation & Sign conventions for lenses and mirrors ¨ The thin-lens equation (for thin ¨ Focal length, �: lenses and mirrors): ¤ + for a converging lens or a concave mirror ¤ − for a diverging lens or a convex mirror 1 1 1 ¨ Magnification, �: + = ¤ + for upright image � �$ � ¤ − for inverted image $ ¨ Image distance, � : ¤ + for a real images ¤ − for a virtual images ¨ Object distance, �: ¤ + always Quiz: 18.7-1 through 18.7-4 10 Demo: lens equation applied for a lens 11 ¨ Image Formation ¤ Demonstration of a double convex lens forming an inverted and diminished or enlarged image. ) ) ) n + = * *+ , ) ) ) n + = , where � is the distance between the light source and the screen. * -.* , 3 -± -1.2-, n � = 4 Quiz: 18.7-5 Example: 18.7-1 (Knight P18.27, modified) 13 ¨ A dentist uses a curved mirror to view the back side of teeth on the upper jaw. Suppose she wants an erect image with a magnification of 2.0 when the mirror is 1.2 cm from a tooth. (Treat this problem as though the object and image lie along a straight line.) A. What is its focal length? B. Is it a convex or concave mirror?.