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physics med 101 > week 9 > Flashcards

week 9 Flashcards

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1
Q

what is light?

A
  • an electromagnetic wave
  • a self-propagating combination of oscillating electric and magnetic fields
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2
Q

visible light ranges between

A

380 and 750 nm

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3
Q

what is refraction?

A

when a ray of light is transmitted obliquely through the boundary between two materials of unlike index of refraction, the ray bends

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4
Q

the absolute index of refraction of a material is defined as

A

n = speed of light in vacuum / speed of light in the material
or
n = c / v

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5
Q

what is the relative index of refraction of material 1 with respect to material 2

A

relative index = n1 / n2

  • n1 and n2 are the absolute refractive indices of the 2 material
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6
Q

what happens when n2 > n1, and what happens when n2 < n1

A
  1. the ray bends toward the normal as it enters the second material
  2. the ray bends away from the normal
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7
Q

what 3 aspects lie on the same plane?

A

the incident ray, refracted ray, and the normal

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8
Q

what are the angles θi and θr called respectively?

A

angle of incidence, angle of refraction

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9
Q

what does Snell’s Law give?

A

the way in which a ray refracts at an interface between materials with indices of refraction (ni) and (nr)

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10
Q

what is the equation of Snell’s Law

A

n1 sinθ1 = n2 sinθ2

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11
Q

what is reflection?

A

when light hits the surface of almost any material, some of that light ‘bounces back’ off the surface

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12
Q

what does the law of reflection state?

A

the reflected light leaves the surface at the same angle that the incident light falls on

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13
Q

equation of the law of reflection

A

θi = θrfl

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14
Q

two ways reflection can be described

A

specular or diffuse

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15
Q

specular reflection

A
  • when light hits a very flat, reflective surface, such as a mirror
  • all light coming from a single direction is reflected in a single direction
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16
Q

diffuse reflection

A

when the surface is rougher, the light is reflected in a wide range of directions

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17
Q

what is total internal reflection?

A

the complete reflection of an incident light ray at a boundary, with no transmission

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18
Q

when does total internal reflection occur?

A

it occurs only for waves incident on a boundary with a medium where the reflective index is reduced

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19
Q

critical angle

A

n1 sinθc = n2 sin90 = n2

θc = sin^-1 n2 / n1

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20
Q

when the angle of incidence is larger than the critical angle

A

none of the wave is transmitted through the boundary, only reflection occurs

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21
Q

what is the requirement for materials to be transparent?

A

visible wavelengths of electromagnetic radiation must pass through without being absorbed

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22
Q

the refractive index is _____ on the shorter wavelength side and _____ on the longer wavelength side

A

higher, lower

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23
Q

what is dispersion? what are dispersive media?

A
  • when the wave speed is depended on the frequency
  • materials with this property are called dispersive media
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24
Q

converging (or positive) lenses are _____ at the center than at the rim, while diverging (or negative) lenses are _____ at the center

A

thicker, thinner

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25
Q

what is the focal point of a thin lens with spherical surfaces?

A

the point f where rays parallel to and near the center or optical axis are brought to a focus

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26
Q

focus is _____ for a converging lens and ______ for a diverging lens

A

real, virtual

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27
Q

what is the focal length (f)

A

the distance of the peripheral focus from the lens

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28
Q

all rays passing through the lens form an image a positive distance d2 to the right of the lens, which is given by the equation

A

1 / d1 + 1 / d2 = 1 / f

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29
Q

when is a real image formed at d2?

A
  • when d1 > f
  • which means that we will see the image at d2 if we place a screen (such as a piece of paper)
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30
Q

converging lenses form inverted real images of objects located where?

A

outside the principal focus

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31
Q

what occurs when the object is between the principal focus and the lens?

A

the image is virtual (on the same side of the lens as the object), erect, and enlarged

32
Q

what parts of the eye are positive lenses?

A

the cornea and crystalline lens
because they need to form a real image on the retina

33
Q

corrective lenses (eyeglasses) can have a positive focal length _____ or a negative focal length _____

A

presbyopia, myopia

34
Q

the power of a lens is the _____, and is measured in _____

A
  • the inverse of its focal length
  • diopters (D)
35
Q

the Lensmaker’s equation is

A

1 / f = (n - 1) ( 1/ r1 - 1/ r2)

36
Q

when is the radius of a curvature (r) positive? when is it negative?

A

positive - when its center of curvature lies to the right of the surface

negative - when its center of curvature lies to the left of the surface

37
Q

what shapes do lenses of positive focal lengths have?

A
  1. biconvex
  2. planoconvex (one side flat)
  3. positive meniscus
38
Q

what shapes do lenses of negative focal lengths have?

A
  1. biconcave
  2. planoconcave
  3. negative meniscus
39
Q

isolated cornea is a

A

a negative meniscus lens

40
Q

the crystalline lens is a

A

an asymmetric biconvex lens

41
Q

which images are inverted? which images are upright

A

real images are inverted
virtual images are upright

42
Q

why is the cornea transparent?

A

because it is uniform in structure, avascular except in the extreme periphery, and relatively dehydrated

43
Q

what is the cornea covered by?

A

a 7-10 µm thick layer of tears
(which smooths over optical irregularities and supplies the cornea with oxygen)

44
Q

what is the average radius of curvature of the anterior surface of the cornea?

A

about 7.8 mm in the central region with a variation of about ±0.4 mm, and is flatter in the periphery

45
Q

the pupil in the iris can vary from ___ to ___ in diameter

A

1.5 to 10 mm

46
Q

what controls the diameter of the pupil?

A

an opposing pair of smooth muscles

47
Q

where is the crystalline lens suspended? how thick is it and what is its diameter?

A
  • it is suspended and rests on the posterior surface of the iris
  • it is about 4mm thick and 9mm in diameter
48
Q

what is the formation of an image on the retina determined by?

A
  1. the indices of refraction of each eye component that the light passes through
  2. the shapes of the surface of these elements in the eye
49
Q

what performs two-thirds of the focusing and what performs the remaining one-third?

A

two-thirds: the cornea
one-third: the crystalline lens

50
Q

describe the rod cells in the retina

A
  • 120 million
  • high sensitivity
  • low spatial acuity (detection of shape)
  • more numerous in the periphery
51
Q

what is the sensitivity of rods? what is the diameter?

A

500 nm, 2µm

52
Q

what two kinds of vision are rods responsible for?

A

night vision and peripheral vision

53
Q

two reasons why visual acuity is decreased in the outer portions of the retina

A
  • rods are far from the fovea
  • many rods are connected to the same nerve fiber
54
Q

describe the cone cells in the retina

A
  • 6.5 million
  • low sensitivity
  • high spatial awareness
  • concentrated in the fovea
55
Q

what are the 3 types of cone cells and their respective spectral sensitivities?

A
  1. blue cones (445 nm)
  2. green cones (535 nm)
  3. red cones (670 nm)
56
Q

when does absorption occur?

A

when the photons have energy in ranges that can be absorbed by the photosensitive molecules (rhodopsin) in these cells

57
Q

only 50% of visible light reaches the retina, what are the reasons behind losses of light reaching the retina?

A
  • reflection of light
  • absorption
  • scattering
58
Q

what does transmission through the retina cause?

A

loss due to absorption and scattering within the retina before light hits the rods and cones

59
Q

what is the reflected fraction at the air/cornea interface?

A

2%

60
Q

most of the light from ___ to ___ nm is absorbed by the crystalline lens

A

300 to 400

61
Q

what are the schematic models for the imaging of rays in the eye?

A
  1. Gullstrand exact eye
  2. Reduced eye
  3. Schematic eye 1
62
Q

Gullstrand exact eye model

A
  • the most complete model
  • has six refractive surfaces
  • the variation of the refractive index within the lens is incuded
63
Q

Reduced eye model

A
  • simplest model
  • only one refractive interface at the cornea
  • all distances are relative to the single refractive surface
64
Q

Schematic eye 1

A
  • the refractive index within the crystalline lens is uniform
  • contains 4 interfaces, 5 refractive indices, and radii of the 4 surfaces
65
Q

what is accommodation?

A

the ability to control the focal length of the crystalline lens

66
Q

what controls the curvature of the crystalline lens surfaces and thus its focal length

A

the tension in the ligaments suspended in the crystalline lens

67
Q

what happens when the tension in ligaments is at a maximum?

A

the crystalline lens flattens and the focal length is at a maximum

68
Q

what will a flatter lens produce? what will a larger curvature of the crystalline lens surface produce?

A
  • clear images of distant objects
  • a shorter focal length, which produces clear images of nearby objects
69
Q

lack of appropriate accommodation is called

A

presbyopia

70
Q

reasons behind the loss of accommodation with age

A
  1. increase in crystalline lens Young’s modulus
  2. flattening of the lens
  3. decrease in the lens capsule Young’s modulus
71
Q

hyperopia

A
  • farsightedness (can see far)
  • due to long focal length, causing the image to be focused behind the retina, making it difficult for the person to see close up
72
Q

myopia

A
  • shortsightedness (can see near)
  • due to short focal length, causing the images of distant objects to be focused in front of the retina
73
Q

a myopic eye is corrected with a _____ lens while a hyperopic eye is corrected with a _____ lens

A

concave, convex

74
Q

the near point has a normal of ___, while the far point has a normal of ___

A
  • 25 cm
  • infinity
75
Q
A

physics med 101 (10 decks)

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