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


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


Check Yourself

What objects in this room radiate light?

Is the projector screen radiating visible light?

Is the screen diffuse or specular reflector?


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


Pinhole Camera

Small pinhole allows only small amount of light in, blocking overlapping diffuse rays and forming image inside the camera.


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


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?


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.


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


Law of Reflection

Angle of incidence equals angle of reflection

SPECULARREFLECTION


Demo: Blackboard Optics

Special blackboard has mounted light source and mirrors.

LightSource

Mirror

Demonstrates theLaw of Reflection

Incident

Reflected


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).


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


Mirror Image Reflection

To observer at point B, the light from point A seems to come from point A’, within mirror.


Plane (Flat) Mirror

Tracing light rays from original, to mirror, to eye allows us to construct image.

Original Image

Mirror

HAIR

NOSE

CHIN


Demo: Pocket Mirror

See full image of your head in a plane mirror that’s half the size of your head.

Original Image

Mirror


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


Non-Flat MirrorsImage in a curved mirror is

distorted from original.Determine image location

and size by ray tracing


Demo: Convex Mirrors

Mirrored surface on a sphere or similar rounded shape. Image is smaller & closer.

MC EscherHand with Reflecting Sphere


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.


Ray Tracing for Convex Mirror

Image in convex mirror is smaller & closer.

Original

Image

Mirror


Image in the Mirror #2

Portrait of Giovanni Arnolfini and his Wife (1434)by Hubert and Jan van EYCK


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


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


Ray Tracing for Concave MirrorImage in concave mirror is larger when

original is close to the mirror.

OriginalImageMirror


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


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


Reflecting Telescopes

Large, modern telescopes form images using concave mirrors.

Hubble’s mirror

MagellanTelescope


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


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.


Demo: Refraction thru Block

Light is refracted entering the block and refracted back on leaving the block.


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


Lenses

Curvature of a lens surface produces a continuous, variable angular refraction.

Concave lens shrinks its image

Convex lens magnifies its image


Demo: Concave Lenses

Curved surface of a concave lens causes light rays to diverge, shrinking images.


Demo: Convex Lenses

Curved surface of a convex lens causes light rays to converge, magnifying images


Demo: Real Image of Convex Lens

Image formed by convex lens can be observed on a screen.


Total Internal Reflection

When refraction angle exceeds 90º the light does not cross the surface.

Refracted

ReflectedReflected


Demo: Total Internal Reflection

Prism demonstrates total internal reflection if the angle of incidence is large enough.


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

http://upload.wikimedia.org/wikipedia/commons/9/92/Black_triggerfish.jpg


Demo: Total Internal Reflection

Past the critical angle all the light is internally reflected.

Just below critical angle


Fiber OpticsTotal internal reflection

causes light to reflect inside a solid glass tube.


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

10-Aug-15 Physics 1 (Garcia) SJSU Chapter 28 Reflection & Refraction.

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Transcript of 10-Aug-15 Physics 1 (Garcia) SJSU Chapter 28 Reflection & Refraction.