18.2 Reflection and Mirrors

1. 18.2 Reflection and Mirrors Pg. 617-622

2. Reflection of Light Rays • The reflection you see in the mirror depends on how the surface reflects the light • Rays are straight lined representations of how light reflects • Light rays obey the law of reflection • The two ways in which a surface can reflect light are regular reflection and diffuse reflection

3. Regular Reflection • When parallel rays of light hit a smooth surface, regular reflection occurs • All the light rays reflect at the same angle • Produces a sharp reflection

4. Diffuse Reflection • When parallel rays of light hit a bumpy or uneven surface, diffuse reflections occur • Light rays hit the surface at different angles because of the uneven surface • Each light ray reflects at a different angle • DO NOT see a clear reflection

6. Plane Mirrors • Plane mirrors are a flat sheet of glass, that has a silver-colored coating on one side • the coating reflects the light • The coating is smooth = regular reflection occurs and a clear image forms • Image is a copy of an object formed by reflected or refracted rays of light

7. What kind of image forms: • Virtual images are upright images that forms where light seems to come from • Virtual = something that does not really exist • Plane mirrors produce virtual images that are upright and the same size as the object • Image not exactly same as object • The left and right of the image are reversed

8. How Images Form • Light rays from the object strike the mirror and reflect towards the observer’s eye • Even though rays are reflected the observer’s brain treats them as if they had come from behind the mirror • Image appears to be behind the mirror

9. Concave Mirrors • A mirror with a surface that curves inward like the inside of a bowl is a concave mirror • Reflects parallel rays of light so that they meet at a point • The Optical Axis is an imaginary line that divides a mirror in half • The Focal Point is the point at which rays parallel to the optical axis meet • Depends on shape of mirror • More curved the mirror the closer the focal point is to the mirror

10. Concave Mirrors • The Optical Axis is an imaginary line that divides a mirror in half • The Focal Point is the point at which rays parallel to the optical axis meet • Depends on shape of mirror • More curved the mirror the closer the focal point is to the mirror

11. X= Focal Point---- = Optical Axis

12. Representing How Images Form • Ray diagrams are used to show where a focused image forms on a concave mirror • Shows rays of light coming from points on the object • Two rays coming from one point on the object meet or appear to meet at the corresponding point on the image ***Turn to pg. 620 to practice drawing ray diagrams***

13. Determining the Type of Image • Concave mirrors can form virtual or real images • If an object is placed at the focal point = NO Image forms! • if the light is placed at the focal point it can project parallel rays of light • Ex. Car headlights

14. Real images form when rays actually meet Occur if the object is farther away from the mirror than the focal point May by larger or small than the object Virtual images form when the object is between the mirror and focal point are always larger than the object for concave mirrors Real Vs. Virtual Images

15. Convex Mirrors • Convex Mirrors are mirrors with surfaces that curve outwards • rays spread out but appear to come to from a focal point behind the mirror • Because rays never meet, images formed by convex mirrors are always virtual and smaller than the object • Used in car mirrors • Advantage: allows you to see a larger area than you can with a plane mirror • Disadvantage: images appears further away than it really is