Phys6 - Light & Optics

  1. Constructive v. Destructive Interference
    • constructive: waves are in phase (additive)
    • destructive: waves are out of phase (if equal in amplitude waves cancel out perfectly)
  2. Interference w/ Light
    • two light waves hit the same spot:
    • if in phase → constructive overlap
    • if out of phase → destructive overlap
  3. dsinθ = (m + 1/2)*λ
    • If light wavelengths are different from each other by some variation of half a wavelength (eg. 1/2, 3/2, etc.) then the resulting light spot will appear DARK →
    • *a dark light spot signifies DEstructive interference
    • m = any integer starting with 0 (1, 2, 3, etc.)
  4. dsinθ = m*λ
    • if the “distance” a light wavelength travels is different from another by some variation of an integer of a wavelength (eg. 1, 2, 3, etc.) then the resulting light spot where the 2 wavelengths converge will appear BRIGHT →
    • *a bright light spot signifies CONstructive interference
  5. Diffraction Grating
    • a surface with slits equidistant all the way across it
    • if light is shone through the surface there are many slits which it can pass through
    • d = distance between adjacent slits
    • equation for diffraction grating is the same as for just a double slit system: dsinθ = m*λ
  6. Speed of Light in a Vacuum
    • cvac = 3 * 108 m/s
    • similar value for the speed of light in air
  7. Index of Refraction (n)
    • n = cvac / vmed
    • cvac: speed of light in a vacuum
    • vmed: velocity of light in whatever medium
    • vmed will NEVER be larger than cvac b/c light will never travel faster than it does in a vacuum
    • therefore the ratio for n will always be bigger than 1
    • n ~ 1 for air
    • n ~ 1.33 for water
  8. When light travels from a LOWER to HIGHER index of refraction, n, what happens to the wavelenght?
    it becomes INVERTED
  9. White Light
    • smear of all wavelengths of light in the visible spectrum
    • if you REMOVE a color from white light (eg. due to destructive interference?) what results is that color’s complimentary color across from it on the color wheel
  10. Mirrors
    • if a mirror is concave → it’s converging
    • if a mirror is convex → it’s diverging
  11. Lens
    • if a lens is convex → it’s converging
    • if a mirror is concave → it’s diverging
  12. Focal Distance
    • always equal to exactly 1/2 the radius of curvature
    • f = 1/2r
  13. Lens Strength
    • 1/f = diopters
    • focal distance HAS to be in meters
    • 1 over the focal distance = Diopters (D) → which corresponds to the strength of a lens
  14. So if a questions gives you a mirror or lens’ radius of curvature, what values can you derive from r?
    • 1. focal length (f) [f = 1/2r]
    • 2. strength of the lens in Diopters [D = 1/f]
  15. Upright v. Inverted
    • if the image comes out below the principle axis → it’s inverted (upside down)
    • if the image comes out above the principle axis → it’s upright
  16. Real v. Imaginary
    • if light rays truly converge at di or a certain point → the image is Real
    • if light rays do not truly converge at any certain point → the image is Virtual
  17. *a Real image is ALWAYS Inverted & a Virtual Image is ALWAYS Upright
    • can remember using the mnemonics:
    • IR spec: Inverted, Real
    • UV light: Upright, Virtual
    • (also remember just it’s counterintuitive - weird opposites)
  18. Equation for Focal Length
    • 1/f = 1/do + 1/di
    • di: distance from mirror to the image
    • do: distance from mirror to the object
  19. Equation for Magnification
    • m = hi / ho or m = – di / do
    • hi: height of the image
    • ho: height of the object
  20. Sign Rules for di & do
    • object will ALWAYS be out in front of the mirror → do is positive (+do)
    • if the image is REAL (i.e. the light rays that form the image actually converge) → di is positive (+di)
    • however if the image is virtual (i.e. the light rays that form the image NEVER actually converge) → di is negative (–di)
  21. How to Interpret Magnification Equation
    • if m is positive → then the image in question is upright
    • if m is negative → then the image is upside-down inverted
    • if the absolute value of m is bigger than 1 → then the image appears bigger than the original object
    • if the absolute value of m is smaller than 1 (eg. 0.5) → then the image appears smaller than the object
  22. What is the focal distance for a diverging MIRROR?
    the focal distance for a diverging MIRROR is NEGATIVE (-f)
  23. For a Diverging Mirror the image is ALWAYS:
    1. Upright

    2. Virtual (UV)

    3. smaller than the original object [regardless of whether the do is smaller or larger than the focal distance (inside or outside f)]
  24. A Diverging Lens:
    • always makes the resulting image look smaller

    • always results in a Upright, Virtual image
  25. Aberration
    • when you’re looking at an image in a mirror or through a lens & it appears a little bit FUZZY
    • there are 2 explanations for why aberrations occur → both have to do with light rays not converging on a single point to form a clear focused image*
  26. Spherical Aberration
    light rays that pass through the outer edges of a lens (aka farther away from the principle axis) don’t quite converge exactly where the image forms? → results in a blurry image
  27. Chromatic Aberration
    • as light of different colors passes through the medium of a lens, the light rays get refracted by the lens
    • the indices of refraction for different colors varies depending of the color → this causes some colors to be refracted more or less (angle of refraction differs)
    • usually what results is the edge of the image appear fuzzily colored
Card Set
Phys6 - Light & Optics
Video Set 6