Light and Optics Flashcards
speed of light
c = f x wavelength
blackbody
- ideal absorber of all wavelengths of light
electromag spectrum
radio 10^9-1 m
microwave 1 m-1 mm
infrared 1 mm-700 nm
visible light 700-400 nm
UV 400-50 nm
X-rays 50-10^-2 nm
gamma <10^-2
when light travels through a homogenous medium, it travels in a line…
rectilinear propagation
law of reflection
Ø1 = Ø2
measured in relation with the normal
Real images in a mirror
- if light actually converges at the position of the image
- ability to be projected onto a screen
virtual images in mirror
- lightly only appears to be coming from the position of the image but does not actually converge there
plane mirror
- flat reflective surfaces
- cause neither convergence nor divergence of light rays
- always creates virtual images
spherical mirrors
- concave or convex
- center of curvature: point on the optical axis located at a distance equal to the radius of curvature from the vertex of the mirror
concave surface
- center of curvature and the radius of curvature are located in front of the mirror
- converging mirrors
convex surface
- the center of curvature and the radius of curvature are behind the mirror
- diverging mirrors
focal length (f)
distance between focal point (F) and the mirror
for all spherical mirrors, focal point = r/2
relationship between key variable in geometrical optics
1/f = 1/o + 1/i = 2/r
f: focal length
o: distance between object and mirror
i: distance between image and mirror
positive image distance i>0
- real image
- image in front of mirror
negative image distance i<0
- virtual
- behind mirror
plane mirrors can be thought of as…
- spherical mirrors w indefinitely large focal distances
- r=f=inf
1/o + 1/i = 0
i = -o
magnification (m)
m = - i/o
negative magnification
inversion
positive magnification
upright image
|m| < 1
image smaller
|m| > 1
image is larger
refraction
- bending of light as it passes from one medium of light to another and changes speed
snell’s law
n = c/v
n: index of refraction
c: speed of light
v: speed of light in medium
n1sinØ1 = n2sinØ2
1: where light comes from
2: where light is entering
when light enters a medium with a higher index of refraction (n2 > n1)…
it bends towards the normal
(sinØ2 < sinØ1, Ø2 < Ø1)
when light enters a medium with a lower index of refraction (n2 < n1)…
it bends away from the normal
(sinØ2 > sinØ1, Ø2 > Ø1)
total internal reflection
- a phenomenon in which all the light incident on a boundary is reflected back into the original material, results w any angle of incidence greater than critical angle Øc
- refraction cannot occur
critical angle Øc
- when light move from higher index to lower index, the refracted Ø2 angle is larger than that of Ø1, bending away from the normal
- as incident angle inc so does refracted angle
- critical angle reached when Ø2=90°
Øc = sin^-1 (n2/n1)
lenses
- lenses refract light while mirrors reflect it
- when working with lenses, there are two surfaces that affect the light path
- lenses cause double refraction before meeting the eye
thin spherical lenses
- 1 focal point on each side
- focal lengths are equal so we speak of one focal length for the lens as a whole
- converging lens thicker at the center and diverging lens is always thinner at the center
1/f = 1/o + 1/i
m = -i/o
real lenses
- thickness cannot be neglected
- focal length related to curvature of the lens surfaces
1/f = (n-1)(1/r1 - 1/r2)
single lens sign conventions
~
+ -
o: object same side as light opposite
i: image opposite side light same
(real) (virtual)
r: convex concave
(converging) (diverging)
f: convex concave
(converging) (diverging)
m: upright inverted
Designations of real and virtual when comparing mirrors and lenses…
- are on opposite sides
- remember, the R side is dependent on where the light goes after interacting w the lens or mirror
- light does through the lens, and so the R side is opposite the light whereas the front is R for a mirror because of reflection
for both mirrors and lenses, converging species have…
(+) focal lengths and radii or curvature
for both mirrors and lenses, diverging species have…
(-) focal lengths and radii of curvature
for thin lenses with negligible thickness, the sign of focal length and radius of curvature…
are given based on the first surface the light passes through
Power
P = 1/f
- diopters
- pos for converging lens nearsighted
- neg for diverging lens farsighted
bifocal lenses
one converging lens hyperopia
one diverging lens myopia
multiple lens system negligible distance
1/f = 1/f1 +…+ 1/fn
P = P1 +…+ Pn
Multiple lens magnification not in contact
m = m1 x m2 … x mn
spherical aberrations
blurring of periphery of an image as a result of inadequate reflection of parallel beams at the edge of the lens
dispersion
- when various wavelengths of light separate from each other
chromatic abberation
- a dispersive effect within a spherical lens
- cars and eyeglasses correct for rainbow halos and splitting of white light
diffraction
- spreading out of light as it passes through a narrow opening or around an obstacle
- interference between diffracted light rays lead to the characteristic fringes in slit-lens and double- slit systems
single slit
- narrow opening size on the order of light wavelengths then light waves spread out, diffract
slit-lens system
- placed between a narrow slit and a screen, a pattern is observed consisting of a bright central fringe with alternating dark and bright fringes on each side
- central bright fringe twice as wide as the bright fringes on the side
- slits become narrower and central max becomes wider
location of dark fringes (minima) slit-lens system
asinØ = n x wavelength
multiple slits
- displacements of the waves add together in interference
- diffracted light rays emerging from parallel slits can interfere with one another
- constructive interference bright maxima
- destructive interference dark minima
position of dark minima in multiple slit system
dsinØ = (n + 1/2) x wavelength
diffraction gratings
- multiple slits in patterns
- create colorful patterns similar to a prism as wavelengths interfere in characteristic patterns
- interference between reflected rays
- DVD surface, bubbles
X-Ray Diffraction
- bending of light rays to create a model of molecules
- often combined with protein crystallography during protein analysis
- dark and light fringes do not take on a linear appearance, but instead a complex 2D image
plane-polarized light
- light in which electric fields of all the waves are oriented in the same direction
- magnetic field vectors are also parallel, plane of electric field dictates that the plane of the electric field identified the plane of polarization
- unpolarized has random orientation of its electric field vectors
- polarizers
circular polarization
- rare
- interaction of light w certain pigments or highly specialized filters
- uniform amplitude but a continuously changing direction
- helical orientation in the propagating wave
- helix has average electrical field vectors and the magnetic field vectors that lie perpendicular to one another with maxima that fall on the outer border of the helix
red
620-750 nm
orange
590-620 nm
yellow
570-590 nm
green
495-570 nm
blue
450-495 nm
violet
380-450 nm
how does the frequency of light change when moving from one medium to another?
it doesn’t
