Chapter 28 Reflection Refraction 28 Feb21 Physics 1

Chapter 28 Reflection & Refraction 28 -Feb-21 Physics 1 (Garcia) SJSU

Specular and Diffuse 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 28 -Feb-21 Physics 1 (Garcia) SJSU 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? 28 -Feb-21 Physics 1 (Garcia) SJSU

Diffuse Surface is Not a Mirror Light rays diffusely scatter in every direction from every spot on the surface. Look at this spot on a diffuse 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. 28 -Feb-21 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. 28 -Feb-21 Physics 1 (Garcia) SJSU

Camera Obscura The 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. Diffuse light 28 -Feb-21 Physics 1 (Garcia) SJSU Artist’s secret drawing weapon?

Drawing Skill or Optical Aids? Was the chandelier drawn by van Eyck using optical aids, such as a camera obscura? 28 -Feb-21 Portrait of Giovanni Arnolfini and his Wife (1434) Physics 1 (Garcia) SJSU by Hubert and Jan van EYCK

Transparent, Reflecting Surfaces Water and glass are transparent but reflect some of the light striking their surface. Can see some of the riverbed 28 -Feb-21 through the water surface. Can see inside the cab through the right window. Strong reflection of the sun on the left window. Physics 1 (Garcia) SJSU

One Way Mirror Discussion Room (Bright) 28 -Feb-21 Bright Room GLASS One way mirror is just clear glass window. Dark Room Reflected light from bright room masks transmitted light from the darkened observation room Physics 1 (Garcia) SJSU Observation Room (Dark)

Law of Reflection Angle of incidence equals angle of reflection SPECULAR REFLECTION 28 -Feb-21 Physics 1 (Garcia) SJSU

Demo: Blackboard Optics Special blackboard has mounted light source and mirrors. Reflected Light Source Incident Demonstrates the Law of Reflection Mirror 28 -Feb-21 Physics 1 (Garcia) SJSU

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). 28 -Feb-21 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? A B C D E MIRROR 28 -Feb-21 Physics 1 (Garcia) SJSU F G

Mirror Image Reflection To observer at point B, the light from point A seems to come from point A’, within mirror. 28 -Feb-21 Physics 1 (Garcia) SJSU

Plane (Flat) Mirror Tracing light rays from original, to mirror, to eye allows us to construct image. HAIR NOSE CHIN Image Original Mirror 28 -Feb-21 Physics 1 (Garcia) SJSU

Demo: Pocket Mirror See full image of your head in a plane mirror that’s half the size of your head. Mirror Image Original 28 -Feb-21 Physics 1 (Garcia) SJSU

Image in the Mirror Image is seen an equal distance from original within a plane mirror. Velazquez, Venus at her Mirror Utamaro, Woman Powdering Her Neck Incorrect Helmut Newton, Bergstrom over Paris Correct 28 -Feb-21 Physics 1 (Garcia) SJSU

Non-Flat Mirrors Image in a curved mirror is distorted from original. Determine image location and size by ray tracing 28 -Feb-21 Physics 1 (Garcia) SJSU

Demo: Convex Mirrors Mirrored surface on a sphere or similar rounded shape. Image is smaller & closer. 28 -Feb-21 Physics 1 (Garcia) SJSU MC Escher Hand 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. 28 -Feb-21 Physics 1 (Garcia) SJSU

Ray Tracing for Convex Mirror Image in convex mirror is smaller & closer. Image Original 28 -Feb-21 Mirror Physics 1 (Garcia) SJSU

Image in the Mirror #2 28 -Feb-21 Portrait of Giovanni Arnolfini and his Wife (1434) Physics 1 (Garcia) SJSU by Hubert and Jan van EYCK

Demo: Concave Mirrors Mirror is on the inner curved surface of sphere or similar rounded shape. Image size and location depends on object’s distance from the mirror. 28 -Feb-21 Physics 1 (Garcia) SJSU 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. 28 -Feb-21 Physics 1 (Garcia) SJSU Focal Point

Ray Tracing for Concave Mirror Image in concave mirror is larger when original is close to the mirror. Original 28 -Feb-21 Mirror Physics 1 (Garcia) SJSU Image

Ray Tracing for Concave Mirror Image 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. Image Original Mirror 28 -Feb-21 Physics 1 (Garcia) SJSU

Demo: Forming a Real Image Locate the image formed in front of a concave mirror using a strong light source and a screen. Candle Image Screen 28 -Feb-21 Screen Physics 1 (Garcia) SJSU

Reflecting Telescopes Large, modern telescopes form images using concave mirrors. Magellan Telescope 28 -Feb-21 Hubble’s mirror 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. Observer sees image Image Actual 28 -Feb-21 Physics 1 (Garcia) SJSU Actual

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. 28 -Feb-21 Physics 1 (Garcia) SJSU

Demo: Refraction thru Block Light is refracted entering the block and refracted back on leaving the block. 28 -Feb-21 Physics 1 (Garcia) SJSU

Check Yourself Which path does light ray take after entering the wedge? A Which path does it take after leaving the wedge? 28 -Feb-21 Physics 1 (Garcia) SJSU D B C WEDGE E F

Lenses Curvature of a lens surface produces a continuous, variable angular refraction. Concave lens shrinks its image 28 -Feb-21 Convex lens magnifies its image Physics 1 (Garcia) SJSU

Demo: Concave Lenses Curved surface of a concave lens causes light rays to diverge, shrinking images. 28 -Feb-21 Physics 1 (Garcia) SJSU

Demo: Convex Lenses Curved surface of a convex lens causes light rays to converge, magnifying images 28 -Feb-21 Physics 1 (Garcia) SJSU

Demo: Real Image of Convex Lens Image formed by convex lens can be observed on a screen. 28 -Feb-21 Physics 1 (Garcia) SJSU

Total Internal Reflection When refraction angle exceeds 90º the light does not cross the surface. d te c a fr e R ed ct fle Re 28 -Feb-21 Physics 1 (Garcia) SJSU Re fle c ted

Demo: Total Internal Reflection Prism demonstrates total internal reflection if the angle of incidence is large enough. 28 -Feb-21 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 28 -Feb-21 Physics 1 (Garcia) SJSU

Demo: Total Internal Reflection Past the critical angle all the light is internally reflected. Just below critical angle 28 -Feb-21 Physics 1 (Garcia) SJSU

Fiber Optics Total internal reflection causes light to reflect inside a solid glass tube. 28 -Feb-21 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 the Cliff House, San Francisco 28 -Feb-21 Physics 1 (Garcia) SJSU