PH 103

Dr. Cecilia VogelLecture 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

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 Same distance behind mirror as object is

in front Generally “front” is side light comes from.

Same size as object Image is flipped over plane of mirror

Left and right are reversed. because front and back are reversed

Images in Plane Mirror

Based on depth perception.

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 2Both 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 MirrorsA 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 MirrorSuppose your face is in front of a concave mirror, as shown.A ray must reflect from the bottom of the mirror to reflect directly back to your eye.A ray from your mouth must reflect higher to reach your eye.