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Light

Chapter 16. Light. Light. The Ray Model of Light was introduced as a way to study how light interacts with matter Ray= a straight line that represents the linear path of a narrow bean of light Rays can change direction if reflected or refracted. Light Sources.

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Light

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  1. Chapter 16 Light

  2. Light • The Ray Model of Light was introduced as a way to study how light interacts with matter • Ray= a straight line that represents the linear path of a narrow bean of light • Rays can change direction if reflected or refracted

  3. Light Sources • There are MANY different sources of light but there are only two TYPES of sources • 1. Luminous Source = an object that emits light (such as the sun or a candle) • 2. Illuminated Source = object that becomes visible as a result of the light reflecting off it (such as the Moon)

  4. Properties of Light • Luminous Flux=the rate at which light energy is emitted from a luminous source • Symbol=P • Units=lumens (lm) • Illuminance = the rate at which light strikes the surface • Symbol = E • Units = lux (lx)

  5. Properties of Light • The illuminance produced by a point source is proportional to 1/r2 (the inverse square law) • Candela (cd) a measure of luminous intensity • Point Source Illumination: E=P/(4πr2 )

  6. More “Stuff” • Speed of Light (c) = 3.00 x 108 m/s • Diffraction = the bending of light around a barrier

  7. Electromagnetic Spectrum • As the wavelength of visible light decreases, the color changes from red to violet • As wavelength decreases, the frequency increases, and the energy of the wave increases

  8. Electromagnetic Spectrum

  9. Primary Colors of Light • Primary colors of light = red, green, and blue • Secondary colors=yellow, cyan, and magenta

  10. Color • Complementary colors = 2 colors of light that can be combined to make white light • Objects appear a certain color because they reflect that color light and absorb all the others

  11. Polarization • Polarization is the production of light in a single plane of oscillation • Malus’s Law = explains the reduction of light intensity as it passes through a secondary polarizing filter • I2= I1 cos2Ѳ

  12. Seeing Light • Observed Light Frequency = the frequency of light as seen by an observer • Fobs=f (1+/- v/c) • Doppler Shift= the difference between the observed wavelength of light and the actual wavelength • ∆λ=(λobs- λ)=+/- (v/c) λ

  13. Doppler Shift • A positive change in λ = red shift • The relative velocity of the source is away from the observer • A negative change in λ = blue shift • The relative velocity of the source is towards the observer

  14. Doppler Shift • Stellar motion • take the spectrum of a star • compare observed wavelengths of absorption lines to lab values (H, Fe, Na, etc.) • calculate star’s radial motion (need distance and tangential angular motion to get space motion) • NO, you won’t have to calculate this!!!

  15. Chapter 17 Mirrors

  16. Videos • Light, Lenses, and Lasers • Telescopes • Archimedes Death Ray

  17. Reflection • Reflection is the change in direction of a wave at an interface between two different media so that the wave returns into the medium from which it originated. • Law of reflection: the angle of reflection=the angle of incidence • θr=θi

  18. Reflection • Specular reflection = when light hits a smooth surface the rays are reflected in parallel • Diffuse reflection = when light hits a surface that is rough (on the level of the wavelength of light) the light scatters

  19. Reflection • Reflected rays of light that enter the eye appear to originate at a point behind the mirror • Virtual image= a type of image formed by diverging light rays • Always on the opposite side of the mirror from the object

  20. Convex vs Concave

  21. Concave Mirrors • If the object is outside the focal length, a concave mirror will form a real, inverted image.

  22. Convex Mirrors • A convex mirror forms a virtual image.

  23. Chapter 18 Refraction and Lenses

  24. Refraction • Refraction= the bending of light as it passes into a new medium • Snell’s Law of Refraction: • n1sinѲ1= n2sinѲ2 • n= index of refraction

  25. Refraction • Index of Refraction= the ratio of the speed of light in a vacuum to the speed of light in that medium • The index of refraction determines how much the light bends/refracts • n=c/v

  26. Total Internal Reflection • Phenomenon that occurs when light traveling from a region of a higher index of refraction to a region of lower index of refraction strikes the boundary at an angle greater than the critical angle such that all light reflects back into the region of higher index • Critical angle = the angle of incidence above which total internal reflection occurs

  27. Total Internal Reflection

  28. Holography • Holography is "lensless photography" in which an image is captured not as an image focused on film, but as an interference pattern at the film. • Typically, coherent light from a laser is reflected from an object and combined at the film with light from a reference beam. • This recorded interference pattern actually contains much more information that a focused image, and enables the viewer to view a true three-dimensional image

  29. Chapter 19 Interference and Diffraction

  30. Interference • Incoherent light = light with unsynchronized wave fronts that illuminates objects with an even, white light • EX: the light you see when you look at objects illuminated by a light bulb • Coherent light= light from two or more sources that add together in superposition to produce smooth wave fronts

  31. Interference • Interference fringes = a pattern of light and dark bands on a screen, resulting from the constructive and destructive interference of light waves passing through two narrow, closely spaced slits in a barrier

  32. Interference • Thin-film interference : a phenomenon in which a spectrum of colors is produced die to the constructive and destructive interference of light waves reflected in a thin film

  33. Diffraction • The phenomenon of diffraction involves the spreading out of waves past openings which are on the order of the wavelength of the wave • Diffraction pattern : a pattern on a screen of constructive and destructive interference of Huygens’ wavelets

  34. Diffraction • Diffraction Grating = a device made up of many single slits that diffract light and form a diffraction pattern that is an overlap of single-slit diffraction patterns • The tracks of a compact disc act as a diffraction grating, producing a separation of the colors of white light.

  35. Color Puzzles • WOOT!

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