Ch. 8: Light and Optics Flashcards
what are the 7 types of waves in the full electromagnetic spectrum from lowest to highest energy?
- radio waves
- microwaves
- infrared
- visible light
- ultraviolet
- X-rays
- gamma rays
what is the range of wavelengths for the visible spectrum of light? what are the corresponding color extremes?
400 m - 700 nm
violet - red
so 700 - 400 is ROYGBIV
how do electromagnetic waves occur naturally?
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
why are electromagnetic waves transverse?
because the oscillating electric and magnetic field vectors are perpendicular to the direction of propagation
defn: visible region
the only part of the electromagnetic spectrum that is perceived as light by the human eye
defn: white
light that contains all the colors in equal intensity is perceived as white
if an object appears red, what colors does it absorb?
all colors of light except red
defn: blackbody
an ideal absorber of all wavelengths of light, which would appear completely black if it were at a lower temperature than its surroundings
defn: rectilinear propagation
when light travels through a homogenous medium, it travels in a straight line
defn: reflection
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
defn: normal
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
defn: real vs. virtual image
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
what is one of the distinguishing features of real images?
the ability of the image to be projected onto a screen
char (2): plane mirrors
cause neither convergence nor divergence of reflected light rays
flat, reflective surfaces
why do plane mirrors always create virtual images?
because the light does not converge at all
the reflected light remains in front of the mirror, but the image appears behind the mirror
what happens to parallel incident light rays after reflection from a plane mirror?
they remain parallel
how does the image appear in a plane mirror?
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
what type of mirrors are most mirrors found in our homes?
plane!
how can you think of plane mirrors within the context of spherical mirrors?
they are like spherical mirrors with an infinite radius of curvature, infinitely larger focal distances
defn + layman’s meaning: center of curvature (C)
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
concave vs. convex
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)
where are the center and radius of curvature for a concave surface? for a convex surface?
CONCAVE = center and radius are located in front of the mirror
CONVEX = center and radius are located behind the mirror
defn: converging vs. diverging mirrors
CONVERGING = concave = cause parallel incident light rays to converge after they reflect
DIVERGING = convex = cause parallel incident light rays to diverge after they reflect
defn: focal length (f)
the distance between the focal point (F) and the mirror
defn: radius of curvature (r)
the distance between C and the mirror
defn: o
the distance between the object and the mirror
defn: i
the distance between the image and the mirror
what are the implications of the image having a POSITIVE distance? a NEGATIVE distance?
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
defn: magnification (m) + what else does m provide?
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
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?
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
defn: negative vs. positive magnification
NEGATIVE = inverted image
POSITIVE = upright image
what are the implications of |m| < 1
|m| > 1
|m| = 1
|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
use + test day approach: ray diagram
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
what are the three important rays to draw when drawing a ray diagram?
- ray parallel to axis (the normal passing through the center of the mirror) –> reflects back through focal point
- ray through focal point –> reflects back parallel to axis
- ray to center of mirror –> reflects back at same angle relative to normal
what type of image does a single diverging mirror form regardless of the object’s position?
virtual, upright, and reduced image
the farther away the object, the smaller the image will be
what do you do if the rays you draw in a ray diagram do not appear to insersect?
extend them to the other side of the mirror, creating a virtual image
mnemonic for image types with a single lens or mirror (assuming o is positive)
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
defn: refraction
the bending of light as it passes from one medium to another and changes speed
is the speed of light through any medium ALWAYS more or less than its speed through a vacuum?
the speed of light through any medium is ALWAYS less than its speed through a vacuum
defn: index of refraction, n
a dimensionless quantity of a medium that describes the speed of light in that medium
value: index of refraction of a vacuum
index of refraction of any other medium
index of refraction for air
index of refraction of a vacuum = 1
index of refraction of any other medium > 1
index of refraction for air = essentially 1
defn: Snell’s law
a way of describing how refracted rays of light act as they pass from one medium to another
what can we take away from snell’s law?
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
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
the refracted angle is larger than the incident angle (so the refracted light ray bends away from the normal)
defn + what happens to refracted light ray: critical angle
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
defn + cause: total internal reflection
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
what are the two important differences between lenses and mirrors?
- lenses refract light while mirrors reflect it
- 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)
Why does a lens have two focal points? does this remain true for thin, spherical lenses?
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
do converging or diverging lenses correlate with farsighted and nearsightedness?
CONVERGING lenses = reading glasses = needed by people who are farsighted
DIVERGING lenses = standard glasses = needed by people who are nearsighted
func: lensmaker’s equation
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
explain how the eye works in the context of lenses
- the cornea acts as the primary source of refractive power bc the change in refractive index from air is so significant
- light is passed through an adaptive lens that can change its focal length before reaching the vitreous humor
- it is further diffused through layers of retinal tissue to reach the rods and cones
- the image has been focused and maximized significantly but is still relatively blurry (our nervous system processes the remaining errors)
what 3 rays should be drawn to find where the image is for a lens?
- ray parallel to axis –> refracts through focal point of front face of the lens
- ray through or toward focal point before reaching lens –> refracts parallel to axis
- ray to center of lens –> continues straight through with no refraction
what should you do if the rays you draw do not appear to intersect in a ray diagram for a lens?
extend them to the same side of the lens from which the light came, creating a virtual image
real vs. virtual images get confusing, for both lenses and mirrors, what is the real side
what does this mean practically
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
the object of a single lens is on the virtual side, does that make the object virtual?
no
for a thin lens where thickness is negligible, the sign of focal length and radius of curvature are given based on what
the first surface the light passes through
defn: hyperopia and myopia
hyperopia = farsightedness
myopia = nearsightedness
defn + example: lenses in contact
a series of lenses with negligible distances between them
example: a contact lens worn on the eye
what happens to images in multiple lens systems when they are not lenses in contact? + examples
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
defn + outcome: spherical abberation
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
defn: dispersion
when various wavelengths of light separate from each other
what are the implications in terms or refraction for the fact that violet light has a smaller wavelength than red light?
- violet light is bent to a greater extent (experiences the greatest amount of refraction) –> is always at the bottom of the spectrum
- red experiences the least amount of refraction, so it is always on top of the spectrum
as light enters a medium with a different index of refraction, does the wavelength of the light change or the frequency?
the wavelength
defn: chromatic abberation
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
defn: diffraction
the spreading out of light as it passes through a narrow opening or around an obstacle
outcome: interference between diffracted light rays
characteristic fringes in slit-lens and double-slit systems
when light passes through a narrow opening, what happens to the light? what happens as the slit is narrowed?
the light waves seem to spread out (diffract)
as the slit is narrowed, the light spreads out more
what happens if a lens is placed between a narrow slit and a screen? + characteristics of the fringes
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
defn + example: interference
when waves interact with each other, the displacements of the waves add together by this process
example: two parallel slits
how does constructive and destructive interference practically appear on the screen in a double-slit experiment?
constructive interference = bright fringes (maxima)
destructive interference = dark fringes (minima)
the bright fringes are halfway between dark fringes
defn + outcome + example: diffraction gratings
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
why do thin films like soap bubbles and oil puddles cause interference patterns?
because light waves reflecting off the external surface of the film interfere with light waves reflecting off the internal surface of the film
defn: x-ray diffraction
uses the bending of light rays to create a model of molecules
take on a complex 2-D image, not a linear appearance
defn: plane-polarized (linearly polarized) light
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
what is the orientation of the electric field vectors of unpolarized light? + 2 examples
random
ex: sunlight, light emitted from a light bulb
defn: polarizer
filter which allows only light with an electric field pointing in a particular direction to pass through
what happens when you combine two polarizers if they are aligned? perpendicular? somewhere in the middle?
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
char (4) + cause: circular polarization
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
