1. Lesson 1

2.  Reflection occurs when light bounces off a surface.  Specular reflection occurs when light reflects off a shiny surface.  Diffuse reflection occurs when light reflects off a rougher surface.  In this unit we will study specular reflection.

3. Plane Mirror shiny + dark - shiny + + dark - - Spherical Mirrors convex concave Here are sideways views of the three types of mirrors we will study in this unit. The positive side of the mirror is the shiny side. We’ll need to know which side is positive when we do math using the mirror.

4.  Ray tracing is a method of constructing an image using the model of light as a ray.  We use ray tracing to construct optical images produced by mirrors and lenses.  Ray tracing lets us describe what happens to the light as it interacts with a medium.

5. A beam of light can be considered to consist of parallel rays of light, all travelling in a straight line.

6. Mathematical rays never change direction. But light rays can change direction when they interact with materials. The figure above shows a light ray undergoing reflection.

7. Plane Mirror +- Incident ray Reflected ray normalA normal is a line that is perpendicular to the mirror.

8.  The angle of incidence of reflected light equals the angle of reflection.   r =  I  Note that angles are measured relative to a normal to the mirror surface. shiny (+)dark (-) plane mirror light source incident ray normal reflected ray rr ii

9.  Sample Problem: A ray of light reflects from a plane mirror with an angle of incidence of 37 o. If the mirror is rotated by an angle of 5 o, through what angle is the reflected ray rotated?  i = 37 0

10.  r = 37 0 5050 5050  i = 42 0  r = 42 0 42 o + 5 o = 47 o relative to horizontal 47 o - 37 o = 10 o rotation of reflected ray

11.  Sample Problem: Standing 2.0 m in front of a small vertical mirror, you see the reflection of your belt buckle, which is 0.70 m below your eyes. What is the vertical location of the mirror relative to the level of your eyes? If you move backward until you are 6.0 m from the mirror, will you still see the buckle, or will you see a point on your body that is above or below the buckle? Explain

12. buckle mirror eye The mirror must be 0.35 m below the level of your eye. If you move backward, you’ll still see the belt buckle, since the triangles will still be similar. 0.70 m 0.35 m 2.0 m rr ii

13.  Optical images produced by mirrors are named according to the following three characteristics. 1. Nature a)real (converging rays) b)virtual (diverging rays) 2. Orientation a)upright b)inverted 3. Size a)true b)enlarged c)reduced

14. We will now construct an image produced by a plane mirror. This constructed image will represent how images of objects are created by the mirror. +- object located 5 cm in front of mirror Image at -5 cm Reflected rays are diverging. Extend reflected rays behind mirror. Name the image: Virtual, upright, true size