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Light

Light . What is it? How does it work? How do we use it?. Dual Nature. http :// www.youtube.com/watch?v=DfPeprQ7oGc Electromagnetic Waves display wave behavior Created by oscillating electric and magnetic fields Electromagnetic Spectrum – range of frequencies of EM waves. EM Spectrum.

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Light

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  1. Light What is it? How does it work? How do we use it?

  2. Dual Nature • http://www.youtube.com/watch?v=DfPeprQ7oGc • Electromagnetic Waves display wave behavior • Created by oscillating electric and magnetic fields • Electromagnetic Spectrum – range of frequencies of EM waves

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

  4. Characteristics • Transverse waves • Nonmechanical • All EM waves travel at the same speed: • c = m/s • Example: Red light with a frequency of Hz has what wavelength?

  5. 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

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

  7. Polarization • Vibrations in a vertical plane – vertical polarization • Vibrations in a horizontal plane – horizontal polarization • Polarization only exists for TRANSVERSE waves!!!

  8. Polarization • When polarized lenses overlap with axes perpendicular, no light passes through!

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

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

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

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

  13. Ray Diagram – Flat Mirror • Produces an UPRIGHT, • VIRTUAL, SAME SIZE • image

  14. 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)

  15. 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!

  16. We can MATHEMATICALLY predict image formation also!!!! = • fis 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 • h’ is image height (it is NEGATIVE for INVERTED images)

  17. Refraction • Defined as the bending of light as it travels from one medium to another • Depends upon the index of refraction of the material…

  18. Refraction • Index of refraction, n, tells us how fast light travels in the medium • nwater = 1.33 (slower) • nglass = 1.5 (slowest) • nair = 1.00 (fastest) • 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

  19. 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.

  20. Diffraction • Waves spread when they pass through an opening

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