PH 103 Dr. Cecilia Vogel Lecture 2

RECALL OUTLINE  Ray model & depth perception  Reflection  law of reflection  mirror images  Polarization REMINDER  Set your clocks ahead one hour Sat night

Ray Model of Light  Light travels in a straight line.  … while in single material  Ray is an arrow in direction of motion  Narrow laser beam travels straight

 Light travels in a straight line.  light from bulb -- each bit travels straight Ray Model of Light  evidence = shadows. No light behind object

Depth Perception  Rays from nearby object strike two eyes at very different angles  Rays from distant object strike two eyes at nearly same angle  Perceive rays as traveling straight to eye

Ray Model  Ray changes direction when it hits a new material  Often some reflected and some refracted  look at transparent surface like water

Geometry for single ray  The normal line is a line perpendicular to the surface between the two materials  Angles  Angle of incidence (  1 ): the angle between the incident ray and the normal  Angle of reflection (  1 ’): the angle of the reflected ray and the normal  Angle of refraction (  2 ): the angle of the refracted ray and the normal  The refracted ray will always refract into the quadrant the light was headed for

Reflection  Reflected Ray obeys law of reflection  angle of reflection = angle of incidence  angles measured relative to normal  normal is perpendicular to surface Compare to ball bouncing. If it comes in perpendicular, it leaves perpendicular (  =0) Otherwise bounces at same angle on other side of normal.

Images in Plane Mirror  Upright =right side up  NOT inverted = upside-down  Same distance behind mirror as object is in front  Generally “front” is side light comes from.  Image is “virtual” because it is behind mirror, where the light isn’t really going  NOT “real” which describes an image where the light really comes into focus

Images in Plane Mirror  Image is same size as object  (looks smaller, because it is farther away)  Image is reversed front to back  so left and right are reversed.

Images in Plane Mirror Depth perception based in ray model. Both the purple and green rays actually come from point P. But... Where do both the purple and the green rays appear to come from?

Images in 2-D corner Reflector  Can see an image in each mirror  Light can reflect from each mirrors, then back to you.  creating images 1 & 2  And also see an image of image 2  Both should be same place Image 1 Image 2 Image 1 Image of image 2 in mirror 1  Then you also see an image of image 1

Even More Reflections still just 2 mirrors!

Images in Curved Mirrors  A curved mirror that has its center farther away from you than its edges is called a concave mirror.  A curved mirror that has its center closer to you than its edges is called a convex mirror

Example Concave Mirror  Suppose your face is in front of a concave mirror, as shown.  A ray from your eye must reflect from the bottom of the mirror to reflect directly back to your eye.  A ray from your mouth must reflect from higher to reach your eye.