Chapter 29 Reflection & Refraction

May 27 – 30Mr. Gaydos

Chapter 29 Notes

I. Introduction: A. Reflection: Waves incident upon a surface,

some or all of the energy bounces back. B. Refraction: Waves incident upon a medium, waves are bent as they enter & travel within the medium.

Chapter 29 Outline

• Reflection Video

• https://www.youtube.com/watch?v=RlSSy8K_Gos&list=PL5C55F4122B03492C

Chapter 29 NotesII. Reflection (Section 29.1) A. When waves strike a boundary surface between two mediums, some or all of the energy bounces back. They Reflect off of the Boundary. B. The amount of energy reflected back vs. the amount of energy transmitted depends on the composition of each medium. C. Total Reflection: Boundary between Medium 1 & 2 very rigid; Medium #2 >> dense than Medium #1 D. Partial Reflection: Boundary between Medium 1 & 2 not very rigid; Medium #2 = or < dense than Medium #1

Chapter 29 Notes

III. Law of Reflection (Section 29.2)A. The Law: Angle of Incidence (Ѳi) = Angle of Reflection (Ѳr) B. What does this mean?A wave leaves a reflecting boundary at the same angle it arrives C. Boundary Conditions 1. Rigid or Flexible? 1. Smooth or Rough? D. Ray Diagrams E. Chapter 29 Problem Set #1

Chapter 29 Notes

• IV. Mirrors: Three Types (Section 29.3) A. Plane (Flat) Mirror

1. Reflecting surface is Flat 2. Line of Sight (LoS)

3. Image Position (Relative to object’s location) 4. Image Size 5. Image’s Orientation

Chapter 29 Notes

IV. Mirrors: Three Types (Section 29.3)B. Concave Mirror 1. Reflecting surface is Bowed away from object

2. Line of Sight (LoS) 3. Image Position (Relative to object’s location) 4. Image Size 5. Image’s Orientation

Chapter 29 Notes

IV. Mirrors: Three Types (Section 29.3)C. Convex Mirror 1. Reflecting surface is Bowed towards from object

2. Line of Sight (LoS) 3. Image Position (Relative to object’s location) 4. Image Size 5. Image’s Orientation

Chapter 29 Notes

V. Diffuse Reflection (Section 29.4) A. Light Reflected off of a “Rough” surface. B. Light is reflected in many directions.

C. Can see light easily from Rough surface but need to be at correct angle to see reflected light from a mirror.

D. Law of Reflection still holds but so many Boundaries, Normals, Angles of Incidence (Ѳi), Angles of Reflection (Ѳr) on rough surface that it may appear that the Law doesn’t hold but it does at the microscopic level

Chapter 29 Notes

VI. Reflection of Sound (Section 29.5)A. Sound Waves are reflected and are subject to the same Law of Reflection as is Light.B. Multiple reflections of sound are called reverberations.

Chapter 29 Notes VII. Refraction (Section 29.6)

A. The bending of a wave front when one side of the wave moves slower than the rest of the wave.

B. As a wave front encounters a boundary, it will bend in towards the extension of the Normal OR outwards away from the Normal depending on the density of the two mediums separated by the boundary.

C. Rays can be drawn perpendicular to the wave fronts to model wave movement & refraction.

Chapter 29 Notes

VIII. Refraction of Sound (Section 29.7)A. Sound waves are bent due to uneven

temperatures that exist in the medium in which sound waves travel.

B. Sound travels faster in warm air.C. Sound can be heard at night better than

during the day? Yes because the sound waves are bent down toward the ground which allows them to travel farther

Chapter 29 Notes IX. Refraction of Light (Section 29.8)

A. Light waves bend when traveling from one medium to another

B. Index of Refraction: 1. The mathematical relationship that defines

the speed of light in a vacuum vs. its speed in a medium.

2. n = speed of light in a vacuum/speed of light in a material

n = LSvac/LSmed C. Snell’s Law:

n sin Ѳ = n’ sin Ѳ’

Chapter 29 Notes

X. Atmospheric Refraction (Section 29.9)A. Speed of Light only 0.03% less than in a vacuum.B. On Hot days Refraction can be noticeable, Mirages may form, especially on hot streets. C. Even though the sun has set, observer can still see it. Why?

Chapter 29 Notes XI. Dispersion in a Prism

A. Light slows down when traveling in a medium. B. The degree of “speed reduction” depends on the medium and the frequency of light.

C. Since different frequencies of light travel at different speeds in a medium, they will be bent at different angles.

D. This difference in angle results in the colors in white light being separated.

E. This process is called dispersion F. The color violet is bent the most, red is

bent the least.

Chapter 29 Notes

XII. The Rainbow: A. Dispersion on an atmospheric scale.B. Water Droplets in the atmosphere act as a multitude of tiny prisms.C. If viewed from an aircraft high enough the rain “bow” would be a complete circle. We see a bow because the ground gets in the way.

Chapter 29 Notes

XIII. Total Internal Reflection (Section 29.12)A. Condition when light rays cannot exit a

medium but are only reflected within the medium.

B. Critical Angle: a. The angle at which a beam of light no

longer emerges from a given medium.b. For water/air interface, the critical

angle from the normal is 48 °.

Chapter 29 Notes• XIII. Total Internal Reflection (Section 29.12)

C. Diamonds 1. Smallest Critical Angle 2. Small angle results in most light entering a

diamond being totally internally reflected. 3. Light entering through one facet (face) is

internally reflected many times before exiting through another facet.

D. Optical Fibers: 1. Light Pipes

2. Employs total internal reflection to carry light along discrete, dedicated paths much like

metallic wires but without the weight, loss and cost.

DiscoveryKey TermsA. Line of Sight: The straight line along which a light ray passes from an object to our eyes allowing us to see the object.B. Reflection: The bouncing of light off of a Boundary Surface. C. Law of Reflection (Ray Diagram) 1. Angle of Incidence (Ѳi) = Angle of Reflection (Ѳr) (in Degrees or Radians) 2. Normal to Reflecting Boundary: A line at 90 degrees to the Boundary Surface 3. Angle of Incidence (Ѳi): The angle an incident light ray makes with the Normal to the boundary surface 4. Angle of Reflection (Ѳr): The angle a reflective light ray makes with the Normal to the boundary surface

Discovery

D. Mirror: A Reflecting Boundary 1. Plane (Flat): A mirror whose reflecting surface is flat. 2. Concave: A mirror whose reflecting surface is curved away from the object. 3. Convex: A mirror whose reflecting surface is curved towards the object. E. Light Pollution: The uncontrolled spread of light where it is not beneficial or desired. F. Noise Pollution: The uncontrolled spread of noise where it is not beneficial or desired.

Discovery G. Critical Angle: The minimum angle of incidence for which a light ray is totally reflected within a medium. H. Dispersion: The separation of light into colors arranged according to their frequency, by interaction with a prism or diffraction grating. I. Mirage: A floating image that appears in the distance and is due to the refraction of light in the earth’s atmosphere. J. Echo: Reflected Sound K. Reverberation: The persistence of sound, as in an echo, due to multiple reflections.

Discovery L. Total Internal Reflection: The 100% reflection (with no transmission) of light that strikes the boundary between two media at an angle greater than the critical angle. M. Virtual Image: An image formed through reflection or refraction that can be seen by an observer but cannot be projected on a screen because light from the object does not actually come to a focus. N. Wave Front: The crest, trough, or any continuous portion of a two dimensional or three dimensional wave in which the vibrations are all the same way at the same time. O. Field of View: The maximum area that an image can be viewed in a mirror by an observer.

Discovery

P. Refraction: The bending of a wave front when one side of the wave moves slower than the rest of the wave. Q. Diffuse Reflection: The reflection of light rays from a rough surface that results in the light rays being reflected in many directions. R. Optical Fiber: A light Pipe that transports light

along a fixed path much like a length of wire.