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physics and math correct deck > Ch. 8: Light and Optics > Flashcards

Ch. 8: Light and Optics Flashcards

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1
Q

what are the 7 types of waves in the full electromagnetic spectrum from lowest to highest energy?

A
  1. radio waves
  2. microwaves
  3. infrared
  4. visible light
  5. ultraviolet
  6. X-rays
  7. gamma rays
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2
Q

what is the range of wavelengths for the visible spectrum of light? what are the corresponding color extremes?

A

400 m - 700 nm

violet - red

so 700 - 400 is ROYGBIV

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3
Q

how do electromagnetic waves occur naturally?

A

a changing magnetic field can cause a change in an electric field and a changing electric field can cause a change in a magnetic field

each oscillating field causes oscillations in the other field completely independent of matter

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4
Q

why are electromagnetic waves transverse?

A

because the oscillating electric and magnetic field vectors are perpendicular to the direction of propagation

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5
Q

defn: visible region

A

the only part of the electromagnetic spectrum that is perceived as light by the human eye

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6
Q

defn: white

A

light that contains all the colors in equal intensity is perceived as white

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7
Q

if an object appears red, what colors does it absorb?

A

all colors of light except red

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8
Q

defn: blackbody

A

an ideal absorber of all wavelengths of light, which would appear completely black if it were at a lower temperature than its surroundings

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9
Q

defn: rectilinear propagation

A

when light travels through a homogenous medium, it travels in a straight line

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10
Q

defn: reflection

A

the rebounding of incident light waves at the boundary of a medium

they are not absorbed by the second medium, they bounce off the boundary and travel back through the first medium

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11
Q

defn: normal

A

a line drawn perpendicular to the boundary of a medium

all angles in optics are measured from the normal, not the surface of the medium

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12
Q

defn: real vs. virtual image

A

REAL = if the light actually converges at the position of the image

VIRTUAL = if the light only appears to be coming from the position of the image but does not actually converge there

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13
Q

what is one of the distinguishing features of real images?

A

the ability of the image to be projected onto a screen

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14
Q

char (2): plane mirrors

A

cause neither convergence nor divergence of reflected light rays

flat, reflective surfaces

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15
Q

why do plane mirrors always create virtual images?

A

because the light does not converge at all

the reflected light remains in front of the mirror, but the image appears behind the mirror

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16
Q

what happens to parallel incident light rays after reflection from a plane mirror?

A

they remain parallel

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17
Q

how does the image appear in a plane mirror?

A

the image appears to be the same distance behind the mirror as the object is in front of it

plane mirrors create the appearance of light rays originating behind the mirrored surface

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18
Q

what type of mirrors are most mirrors found in our homes?

A

plane!

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19
Q

how can you think of plane mirrors within the context of spherical mirrors?

A

they are like spherical mirrors with an infinite radius of curvature, infinitely larger focal distances

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20
Q

defn + layman’s meaning: center of curvature (C)

A

a point on the optical axis located at a distance equal to the radius of curvature (r) from the vertex of the mirror

this would be the center of the spherically shaped mirror if it were a complete sphere

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21
Q

concave vs. convex

A

concave is like looking into a cave (if we were to look from the inside of a sphere to its surface)

convex is the opposite (if we were to look from outside the sphere)

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22
Q

where are the center and radius of curvature for a concave surface? for a convex surface?

A

CONCAVE = center and radius are located in front of the mirror

CONVEX = center and radius are located behind the mirror

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23
Q

defn: converging vs. diverging mirrors

A

CONVERGING = concave = cause parallel incident light rays to converge after they reflect

DIVERGING = convex = cause parallel incident light rays to diverge after they reflect

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24
Q

defn: focal length (f)

A

the distance between the focal point (F) and the mirror

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25
Q

defn: radius of curvature (r)

A

the distance between C and the mirror

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26
Q

defn: o

A

the distance between the object and the mirror

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27
Q

defn: i

A

the distance between the image and the mirror

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28
Q

what are the implications of the image having a POSITIVE distance? a NEGATIVE distance?

A

POSITIVE (i > 0) = it is a real image = the image is in front of the mirror

NEGATIVE (i < 0) = image is virtual = located behind the mirror

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29
Q

defn: magnification (m) + what else does m provide?

A

a dimensionless value that is the ratio of the image distance to the object distance

also gives the ratio of the size of the image to the size of the object

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29
Q

since plane mirrors are like spherical mirrors with infinite focal distances, what is the value of r and f, and what is the relationship between i and o? how can we interpret this physically?

A

r = f = infinity

i = -o

the virtual image is at a distance behind the mirror equal to the distance the object is in front of the mirror

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30
Q

defn: negative vs. positive magnification

A

NEGATIVE = inverted image
POSITIVE = upright image

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31
Q

what are the implications of |m| < 1
|m| > 1
|m| = 1

A

|m| < 1 –> image is smaller than the object (reduced)
|m| > 1 –> image is larger than the object (enlarged)
|m| = 1 –> image is the same size as the object

32
Q

use + test day approach: ray diagram

A

useful for getting an approx. of where an image is

can be helpful for a quick determination of the type of image that will be produced by an object some distance from the mirror (real v. virtual, inverted v. upright, magnified v reduced)

be cautious on test day! easy to mess up

33
Q

what are the three important rays to draw when drawing a ray diagram?

A
  1. ray parallel to axis (the normal passing through the center of the mirror) –> reflects back through focal point
  2. ray through focal point –> reflects back parallel to axis
  3. ray to center of mirror –> reflects back at same angle relative to normal
34
Q

what type of image does a single diverging mirror form regardless of the object’s position?

A

virtual, upright, and reduced image

the farther away the object, the smaller the image will be

35
Q

what do you do if the rays you draw in a ray diagram do not appear to insersect?

A

extend them to the other side of the mirror, creating a virtual image

36
Q

mnemonic for image types with a single lens or mirror (assuming o is positive)

A

UV NO IR

Upright images are always Virtual

NO image is formed when the object is a focal length away

Inverted images are always real

37
Q

defn: refraction

A

the bending of light as it passes from one medium to another and changes speed

38
Q

is the speed of light through any medium ALWAYS more or less than its speed through a vacuum?

A

the speed of light through any medium is ALWAYS less than its speed through a vacuum

39
Q

defn: index of refraction, n

A

a dimensionless quantity of a medium that describes the speed of light in that medium

40
Q

value: index of refraction of a vacuum

index of refraction of any other medium

index of refraction for air

A

index of refraction of a vacuum = 1

index of refraction of any other medium > 1

index of refraction for air = essentially 1

41
Q

defn: Snell’s law

A

a way of describing how refracted rays of light act as they pass from one medium to another

42
Q

what can we take away from snell’s law?

A

when light enters a medium with a HIGHER index of refraction, it bends toward the normal

if light enters a medium with a SMALLER index of refraction, it will bend away from the normal

43
Q

when light travels from a medium with a higher index of refraction to a medium with a lower one, what happens to the refracted angle in relation to the incident angle

A

the refracted angle is larger than the incident angle (so the refracted light ray bends away from the normal)

44
Q

defn + what happens to refracted light ray: critical angle

A

a special incident angle with a paired refracted angle equal to 90 degrees

to refracted light ray: passes along the interface between the two media

45
Q

defn + cause: total internal reflection

A

a phenomenon in which all the light incident on a boundary is reflected back into the original material

results with any angle of incidence greater than the critical angle

46
Q

what are the two important differences between lenses and mirrors?

A
  1. lenses refract light while mirrors reflect it
  2. with lenses, there are two surfaces that affect the light path (the light is refracted twice as it passes from air to lens and from lens back to air)
47
Q

Why does a lens have two focal points? does this remain true for thin, spherical lenses?

A

because light can travel from either side of a lens (so there is a focal point on each side)

for thin, spherical lenses: the focal lengths are equal, so we speak of just one focal length for the lens as a whole

48
Q

do converging or diverging lenses correlate with farsighted and nearsightedness?

A

CONVERGING lenses = reading glasses = needed by people who are farsighted

DIVERGING lenses = standard glasses = needed by people who are nearsighted

49
Q

func: lensmaker’s equation

A

for lenses where the thickness cannot be neglected, the focal length is related to the curvature of the lens surfaces and the index of refraction of the lens BY this equation

50
Q

explain how the eye works in the context of lenses

A
  1. the cornea acts as the primary source of refractive power bc the change in refractive index from air is so significant
  2. light is passed through an adaptive lens that can change its focal length before reaching the vitreous humor
  3. it is further diffused through layers of retinal tissue to reach the rods and cones
  4. the image has been focused and maximized significantly but is still relatively blurry (our nervous system processes the remaining errors)
51
Q

what 3 rays should be drawn to find where the image is for a lens?

A
  1. ray parallel to axis –> refracts through focal point of front face of the lens
  2. ray through or toward focal point before reaching lens –> refracts parallel to axis
  3. ray to center of lens –> continues straight through with no refraction
52
Q

what should you do if the rays you draw do not appear to intersect in a ray diagram for a lens?

A

extend them to the same side of the lens from which the light came, creating a virtual image

53
Q

real vs. virtual images get confusing, for both lenses and mirrors, what is the real side

what does this mean practically

A

where light actually goes after interacting with the lens or mirror

PRACTICALLY

MIRROR: light is reflected, and therefore stays in front of the mirror (real is in front of the mirror, virtual is behind the mirror)

LENSES: real side is side opposite that of the original light source, virtual side is side of the original light source

54
Q

the object of a single lens is on the virtual side, does that make the object virtual?

A

no

55
Q

for a thin lens where thickness is negligible, the sign of focal length and radius of curvature are given based on what

A

the first surface the light passes through

56
Q

defn: hyperopia and myopia

A

hyperopia = farsightedness

myopia = nearsightedness

57
Q

defn + example: lenses in contact

A

a series of lenses with negligible distances between them

example: a contact lens worn on the eye

58
Q

what happens to images in multiple lens systems when they are not lenses in contact? + examples

A

the image of one lens become the object of another lens

the image from the last lens is considered the image of the system

examples: microscopes, telescopes

59
Q

defn + outcome: spherical abberation

A

a blurring of the periphery of an image as a result of inadequate reflection of parallel beams at the edge of a mirror or inadequate refraction of parallel beams at the edge of a lens

outcome: creates an area of multiple images with very slightly different image distances at the edge of the image, which appears blurry

60
Q

defn: dispersion

A

when various wavelengths of light separate from each other

61
Q

what are the implications in terms or refraction for the fact that violet light has a smaller wavelength than red light?

A
  1. violet light is bent to a greater extent (experiences the greatest amount of refraction) –> is always at the bottom of the spectrum
  2. red experiences the least amount of refraction, so it is always on top of the spectrum
62
Q

as light enters a medium with a different index of refraction, does the wavelength of the light change or the frequency?

A

the wavelength

63
Q

defn: chromatic abberation

A

a dispersive effect within a spherical lens

depending on the thickness and curvature of the lens, there may be significant splitting of white light, which results in a rainbow halo around images

64
Q

defn: diffraction

A

the spreading out of light as it passes through a narrow opening or around an obstacle

65
Q

outcome: interference between diffracted light rays

A

characteristic fringes in slit-lens and double-slit systems

66
Q

when light passes through a narrow opening, what happens to the light? what happens as the slit is narrowed?

A

the light waves seem to spread out (diffract)

as the slit is narrowed, the light spreads out more

67
Q

what happens if a lens is placed between a narrow slit and a screen? + characteristics of the fringes

A

a pattern is observed consisting of a bright central fringe with alternating dark and bright fringes on each side

the central bright fringe (maximum) is twice as wide as the bright fringes on the sides, as the slit becomes narrower, the central maximum becomes wider

the bright fringes are halfway between dark fringes

68
Q

defn + example: interference

A

when waves interact with each other, the displacements of the waves add together by this process

example: two parallel slits

69
Q

how does constructive and destructive interference practically appear on the screen in a double-slit experiment?

A

constructive interference = bright fringes (maxima)

destructive interference = dark fringes (minima)

the bright fringes are halfway between dark fringes

70
Q

defn + outcome + example: diffraction gratings

A

multiple slits arranged in patterns

outcome: can create colorful patterns similar to a prism as the different wavelengths interfere in characteristic patterns

example: organization of the grooves on a CD, thin films like soap bubbles, oil puddles

71
Q

why do thin films like soap bubbles and oil puddles cause interference patterns?

A

because light waves reflecting off the external surface of the film interfere with light waves reflecting off the internal surface of the film

72
Q

defn: x-ray diffraction

A

uses the bending of light rays to create a model of molecules

take on a complex 2-D image, not a linear appearance

73
Q

defn: plane-polarized (linearly polarized) light

A

light in which the electric fields of all the waves are oriented in the same direction (their electric field vectors are parallel) –> the magnetic field vectors are also parallel, but this does not dictate polarization

74
Q

what is the orientation of the electric field vectors of unpolarized light? + 2 examples

A

random

ex: sunlight, light emitted from a light bulb

75
Q

defn: polarizer

A

filter which allows only light with an electric field pointing in a particular direction to pass through

76
Q

what happens when you combine two polarizers if they are aligned? perpendicular? somewhere in the middle?

A

ALIGNED = all light that passes through the first passes through the second

PERPENDICULAR = no light gets through at all

IN THE MIDDLE = determined by the angle between the polarizers’ axes

77
Q

char (4) + cause: circular polarization

A

cause: results from the interaction of light with certain pigments or highly specialized fibers

char:
1. uniform amplitude
2. continuously changing direction
3. helical orientation in the propagating wave
4. average electric and magnetic field vectors that lie perpendicular to one another with maxima that fall on the outer border of the helix

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