Chapter 13 Light and reflection Section 1 Characteristics of Light Chapter 13 Light and reflection

Early Concepts of Light Ancient Greek philosophers thought light consisted of tiny particles which could enter the eye to create the sensation of vision.

Early Concepts of Light Socrates and Plato thought vision resulted from streamers or filaments emitted by the eye making contact with an object

Early Concepts of Light Empedocles, who was Greek, taught that light travels as waves Christian Huygens, Dutch scientist, also thought light was a wave

Early Concepts of Light In 1905 Einstein published the photoelectric effect: light consists of particles called photons Scientists now agree light has a dual wave- particle nature meaning it behaves as both

Electromagnetic Spectrum Consists of: 1. Radio Waves 2. Microwaves 3. Infrared (IR) Waves 4. Visible Light 5. Ultraviolet (UV) Light 6. X rays 7. Gamma Rays

Speed of Light 300,000 km/s in a vacuum

Light-Year The distance light travels in one year Example: If a beam of light were to travel around the Earth it would make 7.5 trips around the Earth in one second.

Electromagnetic Waves Wave that is partly electric and partly magnetic. These make up the electromagnetic spectrum

Chapter 12 The Electromagnetic Spectrum

Electromagnetic Waves DO NOT require a medium Made by vibrating electric charges

Electromagnetic Wave Energy These waves carry radiant energy

Electromagnetic Wave Speed All E. Waves travel at 300,000 km/s in a vacuum Called the speed of light

Only a very small part of the total energy given off by the sun reaches Earth. The sun gives off energy as EM waves in all directions. Most of this energy travels away in space.

Electromagnetic Spectrum Consists of: 1. Radio Waves 2. Microwaves 3. Infrared (IR) Waves 4. Visible Light 5. Ultraviolet (UV) Light 6. X rays 7. Gamma Rays

Chapter 22 Section 2 The Electromagnetic Spectrum

Visible Light Spectrum What are the colors of the visible light spectrum?

Section 1 The Behavior of Light Chapter 13 Light

Light and Matter In order for you to see an object, it must reflect light back to your eyes

Light and Matter Objects can: absorb light reflect light transmit light Depends on type of matter

Opaque Material This type of material only absorbs and reflects light No light passes through it You cannot see what is inside an opaque cup

Translucent Material Allows some light to pass though You cannot see clearly through this material but you can see a shape Example: Frosted Glass Window

Transparent Material Transmits almost all the light You can see objects clearly through a transparent material Example: Glass Window

Chapter 13 Light and Reflection Section 2 & Section 3 Chapter 13 Light and Reflection

Reflection The change in direction of an electromagnetic wave (ex: light) at a surface that causes it to move away from the surface Diffuse reflection- light reflected in many different directions from a rough, textured surface Specular reflection- light reflected in one direction from a smooth, shiny surfaces

Angle of incidence- angle made by the incident ray and the normal Angle of reflection- angle made by the reflected ray and the normal angle of incidence = angle of reflection

Mirrors Simplest is a flat mirror Flat mirrors form virtual images Virtual image- image that forms at a point from which light rays appear to come but do not actually come

Concave Mirror A mirror whose reflecting surface is a segment of the inside of a sphere Used when an object needs to be magnified (i.e. a dressing-table mirror)

Convex Mirror A mirror whose reflecting surface is an outward-curved segment of a sphere Take objects from a large field of view and produce a small image Ex: Side-view mirrors on a car

Parabolic Mirrors Eliminate spherical aberration Spherical aberration- occurs when parallel rays converge away from the mirror’s focal point Reflecting telescopes use parabolic mirrors

Chapter 13 light and reflection Section 4 Chapter 13 light and reflection

Additive primary colors Red, blue, and green light These colors when added together produce white light

Subtractive primary colors Colors of magenta, yellow, and cyan When these three primary colors are combined the resulting color is black

Linear Polarization Waves with vertical electric field oscillations are separated from waves with horizontal electric field oscillations This produces a beam of light with waves oriented in the same direction

Linear Polarization cont’d Ex: Polarized sunglasses These cut down on glare