10-aug-15 physics 1 (garcia) sjsu chapter 28 reflection & refraction
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Apr 19, 2023 Physics 1 (Garcia) SJSU
Chapter 28Reflection & Refraction
Apr 19, 2023 Physics 1 (Garcia) SJSU
Specular and Diffuse Reflection
Reflection from most surfaces is diffuse, with incoming light scattered in all directions.
Reflection from mirror surfaces is specular, with light reflecting in one direction.
Mirror
Diffuse reflection Specular reflection
Apr 19, 2023 Physics 1 (Garcia) SJSU
Check Yourself
What objects in this room radiate light?
Is the projector screen radiating visible light?
Is the screen diffuse or specular reflector?
Apr 19, 2023 Physics 1 (Garcia) SJSU
Diffuse Surface is Not a Mirror
Light rays diffusely scatter in every direction from every spot on the surface.
See a light ray from the top of your head reflected from this spot.
Also see light ray from the tip of your nose reflected from this spot.
Look at this spot on a diffuse surface
Apr 19, 2023 Physics 1 (Garcia) SJSU
Pinhole Camera
Small pinhole allows only small amount of light in, blocking overlapping diffuse rays and forming image inside the camera.
Apr 19, 2023 Physics 1 (Garcia) SJSU
Camera ObscuraThe camera obscura (room darkened) dates to ancient times; it was
first detailed in the writings of Leonardo da Vinci. A room is completely sealed from light except for a coin-sized hole in
one wall. An image of the outside world appears projected, upside down and reversed right-to-left, onto a wall opposite the opening.
A portable camera obscura, equipped with a mirror at a 45-degree angle, reflects the image upward and focuses it on a viewing screen.
Artist’s secret drawing weapon?
Diffuse light
Apr 19, 2023 Physics 1 (Garcia) SJSU
Drawing Skill or Optical Aids?
Portrait of Giovanni Arnolfini and his Wife (1434)by Hubert and Jan van EYCK
Was the chandelier drawn by van Eyck using optical aids, such as a camera obscura?
Apr 19, 2023 Physics 1 (Garcia) SJSU
Transparent, Reflecting Surfaces
Water and glass are transparent but reflect some of the light striking their surface.
Can see inside the cab through the right window.Strong reflection of the sun on the left window.
Can see some of the riverbed through the water surface.
Apr 19, 2023 Physics 1 (Garcia) SJSU
One Way Mirror
One way mirror is just clear glass window.
Bright Room Dark RoomDiscussionRoom (Bright)
ObservationRoom (Dark)
GLA
SS
Reflected light from bright room masks transmitted light from the
darkened observation room
Apr 19, 2023 Physics 1 (Garcia) SJSU
Law of Reflection
Angle of incidence equals angle of reflection
SPECULARREFLECTION
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Demo: Blackboard Optics
Special blackboard has mounted light source and mirrors.
LightSource
Mirror
Demonstrates theLaw of Reflection
Incident
Reflected
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Ray Tracing
Light ray from point A is reflected at point B and arrives at point B.
Notice the relationship between point B (where the ray is reflected to) and point B’ (where the ray would go if the mirror wasn’t there).
Apr 19, 2023 Physics 1 (Garcia) SJSU
Demo: Who Do You See?
Which person in the front row sees the guy with the hat (person F) in the mirror?
FA B C D E G
MIRROR
Apr 19, 2023 Physics 1 (Garcia) SJSU
Mirror Image Reflection
To observer at point B, the light from point A seems to come from point A’, within mirror.
Apr 19, 2023 Physics 1 (Garcia) SJSU
Plane (Flat) Mirror
Tracing light rays from original, to mirror, to eye allows us to construct image.
Original Image
Mirror
HAIR
NOSE
CHIN
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Demo: Pocket Mirror
See full image of your head in a plane mirror that’s half the size of your head.
Original Image
Mirror
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Image in the Mirror
Utamaro, Woman Powdering Her NeckVelazquez, Venus at her Mirror
Helmut Newton,Bergstrom over Paris
Image is seen an equal distance from original within a plane mirror.
Incorrect
Incorrect
Correct
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Non-Flat MirrorsImage in a curved mirror is
distorted from original.Determine image location
and size by ray tracing
Apr 19, 2023 Physics 1 (Garcia) SJSU
Demo: Convex Mirrors
Mirrored surface on a sphere or similar rounded shape. Image is smaller & closer.
MC EscherHand with Reflecting Sphere
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Demo: Blackboard Convex Mirror
Can use optics blackboard to trace diverging rays from convex mirror.
Law of reflection still holds but mirror surface is curved.
Apr 19, 2023 Physics 1 (Garcia) SJSU
Ray Tracing for Convex Mirror
Image in convex mirror is smaller & closer.
Original
Image
Mirror
Apr 19, 2023 Physics 1 (Garcia) SJSU
Image in the Mirror #2
Portrait of Giovanni Arnolfini and his Wife (1434)by Hubert and Jan van EYCK
Apr 19, 2023 Physics 1 (Garcia) SJSU
Demo: Concave MirrorsMirror is on the inner curved
surface of sphere or similar rounded shape.
Image size and location depends on object’s distance from the mirror. Telescope
Apr 19, 2023 Physics 1 (Garcia) SJSU
Demo: Blackboard Concave Mirror
Use optics blackboard to trace convergence of rays from concave mirror.
Notice that rays focus to a point (the focal point) then diverge, as with convex mirror. Focal Point
Apr 19, 2023 Physics 1 (Garcia) SJSU
Ray Tracing for Concave MirrorImage in concave mirror is larger when
original is close to the mirror.
OriginalImageMirror
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Image
Ray Tracing for Concave MirrorImage in a concave mirror is inverted if the original
is far away from the mirror.Image is formed in front of the mirror, not within it.
OriginalMirror
Apr 19, 2023 Physics 1 (Garcia) SJSU
Demo: Forming a Real ImageLocate the image formed in front of a concave
mirror using a strong light source and a screen.
Candle Candle
ImageImage
Screen Screen
Apr 19, 2023 Physics 1 (Garcia) SJSU
Reflecting Telescopes
Large, modern telescopes form images using concave mirrors.
Hubble’s mirror
MagellanTelescope
Apr 19, 2023 Physics 1 (Garcia) SJSU
Refraction
Light rays bend (refract) passing from water to air, making objects appear to be shallower and closer to the observer.
Image
Actual
Image
Actual
Observer sees image
Apr 19, 2023 Physics 1 (Garcia) SJSU
Law of Refraction
Light passing from one material to another is refracted by a fractional angle that depends on the optical density of each material.
Angle is smaller in the denser material.
Apr 19, 2023 Physics 1 (Garcia) SJSU
Demo: Refraction thru Block
Light is refracted entering the block and refracted back on leaving the block.
Apr 19, 2023 Physics 1 (Garcia) SJSU
Check Yourself
Which path does light ray take after entering the wedge?
Which path does it take after leaving the wedge?
A
B
C
D
E
F
WEDGE
Apr 19, 2023 Physics 1 (Garcia) SJSU
Lenses
Curvature of a lens surface produces a continuous, variable angular refraction.
Concave lens shrinks its image
Convex lens magnifies its image
Apr 19, 2023 Physics 1 (Garcia) SJSU
Demo: Concave Lenses
Curved surface of a concave lens causes light rays to diverge, shrinking images.
Apr 19, 2023 Physics 1 (Garcia) SJSU
Demo: Convex Lenses
Curved surface of a convex lens causes light rays to converge, magnifying images
Apr 19, 2023 Physics 1 (Garcia) SJSU
Demo: Real Image of Convex Lens
Image formed by convex lens can be observed on a screen.
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Total Internal Reflection
When refraction angle exceeds 90º the light does not cross the surface.
Refracted
ReflectedReflected
Apr 19, 2023 Physics 1 (Garcia) SJSU
Demo: Total Internal Reflection
Prism demonstrates total internal reflection if the angle of incidence is large enough.
Apr 19, 2023 Physics 1 (Garcia) SJSU
Looking up Underwater
Try this when you’re in the pool this summer
Looking straight up you see the sky but outside the 96° cone surface is like a mirror
Apr 19, 2023 Physics 1 (Garcia) SJSU
Demo: Total Internal Reflection
Past the critical angle all the light is internally reflected.
Just below critical angle
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Fiber OpticsTotal internal reflection
causes light to reflect inside a solid glass tube.
Apr 19, 2023 Physics 1 (Garcia) SJSU
The Big Picture
The whole purpose of this course was to open your eyes to the universe.
The most incomprehensible thing about the world is that it is at all comprehensible.Albert Einstein
Camera obscura next to theCliff House, San Francisco