Light

def of light

electromagnetic radiation that is a form of energy & travels

what is the relationship of the electric & magnetic fields in electromagnetic radiation?

perpendicular to each other & to the direction of propagation

def of wavelength

distance between the adjacent peaks of the wave

def of frequency

number of waves passing a given point each second

equation for wavelength & frequency

c = λf

speed of light in a vacuum

3.00 x 10^8 m/s

equation for speed of light NOT in a vacuum

vm = c/n

(n = index of refraction)

visible light is between ____ nm

380-760 nm

def of monochromic light

single wavelength

def of achromatic light

equal mixture of all visible wavelengths ("white light")

what is the photoelectric effect?

the emission of electrons from a metal when light is shined on it

decrease wavelength = increase speed of e-

increase intensity = increase # of e-

Planck's constant

6.626 x 10^-34 J*s

equation for energy of a photon

E = h*f

the cornea absorbs UV___ light, which can lead to ____

C

solar keratitis

the lens absorbs UV___ light, which can lead to ____

A & B

cataracts

the ____ absorbs infared light, which can lead to ____

lens

glass blower's cataract

at short wavelengths, the ____ nature of light is accentuated

quantum

interference, diffraction, and polarization are examples of _____ optics

wave

absorption, fluorescence, and lasers are examples of _____ optics

quantum

the energy of a light wave is determined by its...

amplitude

def of wave

disturbance that propagates through the available space or medium

def of transverse wave

oscillation is perpendicular to the direction of propagation

def of longitudinal wave

oscillation is parallel to the direction of propagation

def of periodic wave

waves that repeat at regular intervals

def of period

length of each repeating cycle of a periodic wave

def of harmonic/sinusoidal wave

a type of periodic wave that can be described by a single sine function (y = A sin p)

what function is used to define harmonic/sinusoidal waves?

y = A sin p

(p = phase)

t or f: the sum/difference of harmonic waves is always a harmonic wave

false

if 2 or more harmonic waves have the same frequency, then their sum will also be a harmonic wave

if 2 or more harmonic waves have different frequencies, then their sum will NOT be a harmonic wave

when a phase represents space, what is the period?

wavelength

when a phase represents time, what is the period?

temporal period (T)

what is the relationship between temporal period & frequency?

f = 1/T

equation for phase difference (hint: there are 2)

phase represents space: (distance/lamda)*2π

phase represents time: (interval/T)*2π

what is the phase difference between a crest of a wave & the neighboring trough? (assume harmonic wave)

π

what is the wavelength of a harmonic wave? (in radians)

2π

what is the distance between a crest of a wave & the neighboring trough? (assume harmonic wave)

lambda/2

what is the time difference between a crest of a wave & the neighboring trough? (assume harmonic wave)

T/2

equation for velocity of a wave

v = wavelength * frequency

v = wavelength / temporal period

t or f: wavelength AND frequency change when light enters a new medium (with a different index of refraction)

false, wavelength changes but frequency does not

t or f: when light enters a new medium, its color changes due to its change in wavelength

false, color is based on what the wavelength is in a vacuum

t or f: all harmonic waves are sinusoidal waves, but not all sinusoidal waves are harmonic waves

false, it is the other way around

all sinusoidal waves are harmonic

however, not all harmonic waves can be described using a sine function

def of intensity

energy of a wave, per unit area, per unit time

equations for intensity & amplitude

I = A^2

what is the equation for relative intensity?

Irel = I2 / I1 = (A2 / A1)^2

what is another term for intestity?

irradiance

equations for superposition (2)

yr = y1 + y2

Ar sin pr = A1 sin p1 + A2 sin p2

equation for constructive interference

p1 = p2

constructive interference is _____ phase

destructive interference is ______ phase

constructive: in phase

destructive: out of phase (by 180 degrees)

in order to have constructive interference, you need... (2)

same frequency & in phase

in order to have destructive interference, you need... (2)

same frequency & out of phase (by 180*)

what is the relationship between p1 & p2 in constructive interference?

p1 = p2

what is the relationship between p1 & p2 in destructive interference?

p2 = p1 + 180*

def of interference

the combination of 2 or more waves with the same frequency to form a resultant wave in which the displacement is either reinforced or canceled

in a ripple tank, the locations with destructive interference are called _____

locations with constructive interference are called ______

destructive: minima

constructive: maxima

incoherent vs. coherent light sources

coherent = the difference between the phase is constant

incoherent = the difference between phases is constantly changing

for light to have interference, the two sources have to be...

coherent

equation for resultant intensity of coherent waves

Ir = Ar^2

Ir = A1^2 + A2^2 + 2A1A2cos(p1-p2)

equation for average resultant intensity of incoherent waves

Ir (avg) = I1 + I2

when 2 harmonic waves of DIFFERENT frequencies are superposed, what is the resultant waveform?

periodic, but not harmonic

in Young's double-slit experiment, constructive interference corresponds with...

illuminated bands (maxima)

in Young's double-slit experiment, destructive interference corresponds with...

unilluminated bands (minima)

Young's slit experiment revealed what property of light?

wave

if light only had particle property, what would Young's experiment had looked like?

only 2 lines of light would appear

why does Young's experiment support the wave model of light?

multiple lines of light appear on screen, which is an interference pattern formed by a wave

the distance between the 2 slits in a double-slit experiement is designated by the letter...

h

the distance between the screen and the slits in a double-slit experiment is designated by the letter...

t

the distance between the center of the screen to a point of interest on the screen in a double-slit experiment is designated by the letter...

x

the path difference between the 2 sources in a double slit experiment is designated by the letter...

w

what are the equations for w in a double-slit experiment?

w = mλ

(m = order of the fringe)

w = xh/t

what is the equation for x (linear location of a fringe) in a double-slit experiment?

x = mλt / h

what is the equation for θ (angular location of a fringe) in a double-slit experiment?

θ = mλ / h

maxima appear at m = ...

0, 1, 2, etc

minima appear at m = ...

0.5, 1.5, 2.5, etc

linear separating of fringes equation

s = λt / h

angular separation of fringes equation

δθ = (lamba) / h

if wavelength is increased, fringe separation _____

increases

if wavelength is decreases, fringe separation _____

decreases

if distance to the screen (t) is increased, then fringe separation ____

increases

if slit separation (h) is decreased, then fringe separation ____

increases

θ λ δ

when is acuity testing by interference fringes used?

to determine whether someone is a good candidate for cataract surgery or not

what is the minimum intensity (Imin) for a partially coherent wave?

Imin = x% 0 + (1-x%) (2I1)

what is the maximum intensity (Imax) for a partially coherent wave?

Imax = x% (4I1) + (1-x%) (2I1)

what happens to the visibility/contrast of the interference fringes if the light is partially coherent?

reduced

equation for the contrast of partially coherent light

contrast = (Imax - Imin) / (Imax + Imin)

the degree of coherence is the same value as...

fringe visibility

degree of coherence is reported using _____, while fringe visibility is reported using ____

degree of coherence = percent

fringe visibility = decimal

when the maximum from one interference pattern lines up with the minimum from the other, what happens to the fringe visibility?

drops to 0

what is the relative intensity of 2 interference patterns? (lateral coherence effect)

Ir = Ip1 + Ip2

(if there are more than 2, continue to add them together)

to observe interference with better visibility, the angular size needs to be ___(larger/smaller)___

smaller

θs << λ/h

to observe interference with better visibility, the slit separation needs to be __(larger/smaller)___

smaller

h << θs/λ

when θs gets larger, what happens to the interference pattern?

more misaligned. (decreased visibility)

θs represents...

angular size of light source

equation for lateral coherence length

Lw = λ/θs

what does Lw (lateral coherence length) represent?

maximum slit separation (h) for visible fringes

def of light diffraction

light bending around an object

in order to observe diffraction, what conditions need to be met by the opening & the wavelength?

opening needs to be smaller than the wavelength

(smaller openings & longer wavelengths work best)

def of diffraction grating

an array of identical, equally-spaced slits

equation for path difference between neighboring slits

w = h sin θ

when adding a third slit, how does this change the number of maxima?

does not change

when added a third slit, how does this change the number of minima?

doubles