What is it? How does it work? How do we use it?

What is it? How does it work? How do we use it?

Dual Nature http://www.youtube.com/watch?v=dfpeprq7ogc o Electromagnetic Waves display wave behavior o Created by oscillating electric and magnetic fields o Electromagnetic Spectrum range of frequencies of EM waves

EM Spectrum o Visible light the range of EM that produces light that we can detect o Radio and Microwaves are produced by placing a magnetic field in an oscillating electric field o X-rays are produced when fast-moving electrons strike a metal target o Infrared from the sun is responsible for the heating from the sun o Gamma rays are emitted during nuclear collisions

Characteristics o Transverse waves o Nonmechanical o All EM waves travel at the same speed: o c = 3.0 10 8 m/s o Example: Red light with a frequency of 4.5 10 14 Hz has what wavelength?

Mirrors - work by reflection Concave - convergent (all rays come together) Real focal point (the rays REALLY intersect) Convex divergent (all rays spread apart) Virtual focal point (the rays SEEM to intersect behind the mirror) Produces virtual images only

Lenses - work by refraction Convex convergent Real focal point Concave divergent Virtual focal point Produces virtual images only

Polarization o Vibrations in a vertical plane vertical polarization o Vibrations in a horizontal plane horizontal polarization o Polarization only exists for TRANSVERSE waves!!!

Polarization o When polarized lenses overlap with axes perpendicular, no light passes through!

Color Perception o We all see color in different ways. o When light reaches our eyes, we do not see just one frequency, but a variety of frequencies at various intensities. o For example, white light is NOT a color! o It is the presence of all frequencies of visible light o NOT the only way to produce white light! o Primary Colors any three colors that combine to form white light

Color Mixing o Most common primaries are red, green and blue o Yellow, magenta, and cyan are secondary colors o Colors add to form white light o Colors subtract to form black!

Color Mixing - myths o Myth No one set of colors can produce all other colors o Almost any three colors can be mixed to produce the other colors o Colors can be mixed to get even the primary colors! o They will never be as pure as the original frequency o Red, yellow, and blue are not even the best primary set!

Reflection o When light encounters a different substance, part of the light is absorbed while the rest is REFLECTED! o Texture of a surface determines how much reflection o For flat mirrors: angle of incidence = angle of reflection θ = θ

Ray Diagram Flat Mirror o o o Produces an UPRIGHT, VIRTUAL, SAME SIZE image

Drawing Ray Diagrams allows us to predict the location of an image Light can be approximated as rays! Light produces two types of images: REAL these appear in front of the mirror on a ray diagram In reality, REAL images can be projected onto walls and screens VIRTUAL these appear behind the mirror on a ray diagram In reality, VIRTUAL images can only be seen by looking into the mirror Ray diagrams help us predict image location, orientation, similarity, and type of image (LOST)

Rules (Curved Mirrors): Draw all rays from the top of the object. The radius of curvature is the center of your circle; the focal point is HALF that value. Use a ruler and be exact. RAY 1: Draw parallel to the principal axis, reflect through the focal point. RAY 2: Draw through the focal point, reflect parallel to the principal axis RAY 3: Draw through the radius of curvature; reflect back on itself. Image appears where the three reflected rays intersect!

We can MATHEMATICALLY predict image formation also!!!! 1 = 1 + 1 f p q = q h p f is the focal point of the mirror and is HALF the radius of curvature (it is NEGATIVE for a CONVEX mirror) p is object distance from the mirror q is image distance from the mirror (it is NEGATIVE for a VIRTUAL image) h is object height M = h h is image height (it is NEGATIVE for INVERTED images)

Refraction o Defined as the bending of light as it travels from one medium to another o Depends upon the index of refraction of the material

Refraction Index of refraction, n, tells us how fast light travels in the medium n water = 1.33 (slower) n glass = 1.5 (slowest) n air = 1.00 (fastest) n ice = 1.309 Tells me how the light will bend: Fastest to slower, light bends TOWARD THE NORMAL Air to water Slower to faster, light bends AWAY FROM THE NORMAL Water to air

Examples : Draw refracted ray air water air water

Index of refraction As n gets bigger, light moves slower n = c v Snell s Law lets you calculate how much light will bend (refract) when it goes across a boundary. n 1 sinθ 1 =n 2 sinθ 2

Examples: 1. How fast does light travel in glass? c = 3.0 x 10 8 m/s n glass = 1.5 v =? Light travels from air to glass at an angle of 15 degrees. At what angle will the light refract? n 1 = 1.00 (air) n 2 = 1.5 (glass) θ 1 = 15 θ 2 =?

Lens Ray Diagrams Ray 1: Parallel to the principal axis to middle of lens. Refract through BACK focal point. Ray 2: Through the FRONT focal point to middle of lens. Refract parallel to principal axis. Ray 3: Through lens center.

Diffraction Waves spread when they pass through an opening

Review Color Why does an orange look orange? RGB and CMYK Lenses and Mirrors Real world examples Ray diagrams to include LOST When are values positive, negative? Which are diverging, converging Which for farsightedness? EM Spectrum Which colors, types of waves have higher frequencies, higher wavelengths, greater energy

Review Polarizers what do they do? Vocabulary Know all of it! Flat Mirrors Be able to label the diagram Where does an image appear? Index of refraction Light travels fastest in gases, slowest in solids Bigger n value, slower the speed of light What does critical angle mean? What if I go over it? When will light bend toward normal?