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Physics Lesson Plan Teacher Howard Unit Title Refraction Length 75 Goal(s)/PLO(s): Course Grade Level Block/Period identify any of the following from an appropriate diagram: principal axis principal focus focal length focal plane identify a lens as converging (convex) or diverging (concave) Phys 11 11 C Date Class Size Lesson #, of Fri May 21 24 15-2 conduct an experiment to determine the focal length of a convex lens draw accurate scale diagrams for both convex and concave lenses to show how an image is produced describe the characteristics of images produced by converging and diverging lenses Materials: Ray box, lenses, rulers, protractors, drinking straws, tape, model eye convex lenses worksheet Timeline Class Activities Introduction Body Notes 15-2 (omit combination of lenses) Demo 4, 5 (OR QUICK LAB), 6 Closure Notes 15.2 Lenses When light refracts through a pane of glass the light is refracted towards and away from the normal by the same amount. The direction of the ray did not change, it is just offset. If the surface is curved the alignment of the normal is different at different points so the direction of the refracted ray changes from point to point. Lens • Object with at least one curved surface that refracts light • Demo 4 and 5 show concave and convex lens refracting light o Do it from both sides to show that there are 2 focal points but one focal length o Draw 15-7 o geometric-optics_en.jar Ray diagrams can be used to locate the image Ray Parallel Central Focal Ray Parallel Central Focal From object to lens Parallel to principal axis To the centre of the lens Passes through the focal point F From object to lens Parallel to principal axis To the centre of the lens Toward back focal point F From converging (vex) lens to image Passes through focal point F From the centre of the lens Parallel to the principal axis From diverging (cave) lens to image Directed away from focal point F From the centre of the lens Parallel to the principal axis There are six possible types of images for a converging lens depending on the location of the object (sketch figure 15-3 with the descriptions) 1. object at infinity, image at F (burning ants) 2. Object outside 2F, real, small image between F and 2F. (camera or eye lens) 3. Object at 2F, real image at 2F same size as the object (inverting telescope) 4. Object between F and 2F, real, magnified image outside 2F (movie projector) 5. Object at F, image at infinity (searchlights) 6. Object inside F, magnified virtual image on same side of the lens as the object (telescope or magnifying glass) Diverging lenses only produce virtual images (draw 15-9) The magnification equation still applies (image/object) People who’s eyes do not focus properly can be helped by wearing glasses or contact lenses • Demo with model eye Farsighted (see far things well) • Hyperopia • Eye is too short • Corrected with a converging lens Nearsighted (see near things well) • Myopia • Eye is too long • Corrected with a diverging lens Assign worksheet