PHYS 1260 Exam 4 with correctly explained test.
Superposition and Interference - -- same wave + same wave = reinforcement
- two opposite waves = cancellation
- two similar waves = partial cancellation
- interference patterns of overlapping waves from 2 vibrating sources
- interference pattern = caused by interference b/w a pair of waves
- constructive interference produces bright region where waves reinforce each other
(waves arriving in phase)
- destructive interference produces dark region where waves cancel each other (waves
arriving half a wavelength out of phase)
- a monochromatic light into double slits produces an interference pattern
- the phenomenon of interference occurs for = sound waves + light waves --> interference is
the property that characterizes waves in general
Superposition and Interference part 2 - -- single-color thin-film interference =
reflection from the upper and lower surfaces of a wedge of air b/w 2 glass plates
- interference colors by reflection from thin films = the thin film of gasoline is just the right
thickness to result in the destructive interference of blue light
- diffraction grating = composed of a large number of close, equally spaced slits for
analyzing light source; produced by spectrometers that disperse white light into colors
- if the thin film of gasoline was a bit thinner, the wavelength to be canceled would be =
shorter than that of blue
- if violet light were canceled by the double reflection of sunlight from gasoline on a wet
surface, the resulting color would likely be = orange --> orange is the complementary color
of violet
- if you see the color blue reflected in the interference from gasoline on water, and you
lower your head so a greater angle from the normal results, you'll likely see a color having a
wavelength = shorter than that of blue --> the path through the gasoline would be longer,
and a longer wavelength would be canceled; the result of a long wave being canceled is a
shorter wave
superposition and interference part 3 - -interference colors = that colors are
subtractive primaries = magnetas, yellows, and cyans
double-slit experiment - -- monochromatic light passing through 2 slits, a, forms an
interference pattern, b, shown graphically in c
, PHYS 1260 Exam 4 with correctly explained test.
- suppose we dim our light source so that, in effect, only 1 photon at a time reaches the
barrier w/ the thin slits
- if film behind the barrier is exposed to the light for a very short time, the film gets exposed
= each spot represents the place where the film has been exposed by a photon; if the light
is allowed to expose the film for a longer time, a pattern of fringes begins to emerge
- if we cover one slit so that photons striking the photographic film can pass only through a
single slit, the tiny spots on the film accumulate to form a single-slit diffraction pattern; we
find that photons hit the film at places they would not hit if both slits were open
how do photons traveling through one slit "know" that the other slit is open and avoid
certain regions, proceeding only to areas that will ultimately fill to form an interference
pattern? - -- each single photon has wave properties as well as particle properties
- the photon displays different aspects at different time
- a photon behaves as a particle when it is being emitted by an atom or absorbed by
photographic film or other detectors, and behaves as a wave in traveling from a source to
the place where it is detected
- so the photon strikes the film as a particle but travels to its position as a wave that
interferes constructively
motion is relative - -- the place from which motion is observed and measured is a
*frame of reference*
- *an object may have different velocities* relative to different frames of reference
- to measure the spd of an object, we first choose a frame of reference and pretend that we
are in that frame of reference standing still = then we measure the spd w/ which the object
moves relative to us - that is, relative to the frame of reference
michelson interferometer - -- a beam of light from a monochromatic source was
separated into 2 beams w/ paths at right angles to each other; these were reflected and
recombined to show whether there was any difference in avg spd over the 2 back-and-forth
paths
- the interferometer was set w/ one path parallel to the motion of earth in its orbit
- either michelson or morley carefully watched for any changes in avg spd as the apparatus
was rotated to put the other path parallel to the motion of earth
- but no changes were observed
postulates of special theory of relativity - -- all laws of nature are the same in all
uniformly moving frames of reference
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