Video: The Mirror http://vimeo.com/6212004 Unit #3 - Optics 11.1 - Mirrors Geometric Optics the science of how light reflects and bends optical device is any technology that uses light A) The Law of Reflection When light reflects off a surface, the angle of incidence is always equal to the angle of reflection angle of incidence θi = θr normal i r angle of reflection mirror angle of incidence equals 45, then the angle of reflection Define each: pg 418 normal reflecting surface (mirror) i 1 incident ray incident ray reflected ray angle of incidence angle of reflection 90 θ i1 θ r1 normal reflected ray r 1 applications - bicycle lights - grocery store check-out θi = θr igure 11.22 A sample drawing - change rooms
Mirrors Smooth, shiny surfaces allow you to see an image image is a reproduction of an object produced by an optical device Real - locate on screen x Virtual - formed by rays that do not come from the image Plane mirrors definition: has a flat reflective surface the image has 4 characteristics: - Size - same Ray Diagrams in a Plane Mirror - Attitude - upright; laterally inverted - Location - behind mirror; same distance away - Type - Virtual - appears in the mirror 4 Steps: Part 1: Finding the Image 1. draw perpendicular line from object to mirror 2. extend line equal distance behind mirror Mirror Object 5 cm 5 cm Virtual Image
4 Steps: Part 1: Finding the Image 1. draw perpendicular line from object to mirror 2. extend line equal distance behind mirror Part 2: The Rays 3. draw cone of rays from image to eye 4. draw the incident rays from object to mirror Mirror Object Virtual Image Note: for larger objects, draw rays for each point measured Concave Mirrors ist10_ch11.qxd 7/22/09 3:53 PM Page 421 Spherical mirrors can be thought of as a portion of a sphere which was sliced away and then silvered on one of the sides to form a reflecting surface. Concave Mirror Concave Mirrors A concave mirror, also called a converging mirror, curves inward like a bowl (Figure 11.10). The image fo concave mirror depends on how far the object is from the mirror. If the object is far away from the focal poin rays form an inverted image as shown in Table 11.1. T object gets to the focal point, the larger the image beco is between the focal point and the mirror, like the bird the image becomes upright and enlarged. When the ob the focal point, all rays that leave the object reverse dir mirror and are reflected away from the mirror parallel this case, no image is formed. C = Centre of Curvature converging mirror surface that curves inward like a bowl F Figure 11.10 Table 11.1 Ray Diagrams for Concave Mirrors
Terms Define each: pg. 420 Principal Axis Vertex ray 2 ray 1 h i h o object F d o f vertex principal axis Ray Diagrams in a Concave Mirror Focal Point image d i Focal Length Diagrams Recall that: image is a reproduction of an object produced by an optical device Real - locate on screen Virtual - formed by rays that do not come from the image 3 Rules for Drawing Diagrams rays parallel to principle axis, goes through FP rays through FP, reflects parallel to principle axis ray passing through C of C reflects back on same path Image is located at point of intersection image formed depends on how far the object is from the focal point moves closer becomes larger far away inverted at focal point NO image in front of focal point upright and enlarged; virtual
Applications Mirror Applets Magnification Concave Applet how large or small the image is compared to the object a ratio of height of image to height of the object can be determined by one of two formulas: Magnification = image height object height Magnification = image distance object distance M = h i ho M = d i do
Examples Homework A watch is shinning in a concave mirror 20 cm away. A virtual image is produced 50 cm from the mirror. What is the magnification? An electron microscope magnifies a virus that is 3.50 10 7 m. If the magnification is 3.70 10 5, how big will the image be? Page 423-425 Qu #1 for each group Activity: D15 - Concave Mirrors pg. 430-431 questions Lab Report (Due on Tuesday) Purpose: re-write the one in the text (430-431) Materials: refer to text Method: refer to text Observations: Table and any other relevant notes Lab Intro Video Discussion: Procedure #8-10; Sources of Error Conclusion: answer the purpose. Convex Mirrors Diagrams aka - diverging mirror spreads out the rays
3 Rules for Drawing Diagrams parallel to the principal axis, reflects back as an extension from focal point Drawing a Co You can follow th convex mirror. travels toward the focal point, and direct back parallel ray 1 ray 2 travels toward the centre of curvature, reflect right back F Image is located at point of intersection Applications larger field of view smaller images