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History of the Speed of Light ( c )
History of the Speed of Light ( c )
Introduction
Introduction
Is the Speed of Light Infinite
Is the Speed of Light Infinite
1667 Lantern Experiment
1667 Lantern Experiment
Longitude and Jupiters Moons
Longitude and Jupiters Moons
1676: First Hard Evidence For the Finite Speed of Light
1676: First Hard Evidence For the Finite Speed of Light
1728 Bradley and Stellar Aberration
1728 Bradley and Stellar Aberration
Fizeaus 1849 Cogwheel Experiment
Fizeaus 1849 Cogwheel Experiment
Fizeaus 1851 Water Experiment
Fizeaus 1851 Water Experiment
Maxwells 1865 Theoretical Conclusion
Maxwells 1865 Theoretical Conclusion
Maxwells 1865 Theoretical Conclusion
Maxwells 1865 Theoretical Conclusion
Maxwells 1865 Theoretical Conclusion
Maxwells 1865 Theoretical Conclusion
Foucaults Method Introduced in 1875
Foucaults Method Introduced in 1875
Michelsons 1878 Rotating Mirror Experiment
Michelsons 1878 Rotating Mirror Experiment
The Michelson Interferometer
The Michelson Interferometer
1887 Michelson-Morley Experiment
1887 Michelson-Morley Experiment
1891: Blondlots Parallel Wires
1891: Blondlots Parallel Wires
L. Essens 1950 Microwave Cavity Resonator
L. Essens 1950 Microwave Cavity Resonator
Froomes 1958 Four-Horn Microwave Interferometer
Froomes 1958 Four-Horn Microwave Interferometer
Classroom Application: Microwaving Marshmallows
Classroom Application: Microwaving Marshmallows
History of the Speed of Light ( c )

: David M. Askey. , . , History of the Speed of Light ( c ).ppt zip- 533 .

History of the Speed of Light ( c )

History of the Speed of Light ( c ).ppt
1History of the Speed of Light ( c ). 11mirror.
Jennifer Deaton and Tina Patrick Fall 1996 12Michelsons 1878 Rotating Mirror
Revised by David Askey Summer RET 2002. Experiment. German American physicist A.A.
2Introduction. The speed of light is a Michelson realized, on putting together
very important fundamental constant known Foucaults apparatus, that he could
with great precision today due to the redesign it for much greater accuracy.
contribution of many scientists. Up until Instead of Foucault's 60 feet to the far
the late 1600's, light was thought to mirror, Michelson used 2,000 feet.. Using
propagate instantaneously through the this method, Michelson was able to
ether, which was the hypothetical massless calculate c = 299,792 km/s . 20 times more
medium distributed throughout the accurate than Foucault . Accepted as the
universe. Galileo was one of the first to most accurate measurement of c for the
question the infinite velocity of light, next 40 years. Picture credit.
and his efforts began what was to become a 13The Michelson Interferometer.
long list of many more experiments, each Monochromatic light split and sent it
improving the accuracy of c. along 2 different paths to the same
3Is the Speed of Light Infinite? detector where the 2 waves will
Galileos Simplicio, states the constructively or destructively interfere.
Aristotelian (and Descartes) position, If one path is an integral number of
Everyday experience shows that the half-wavelengths longer than the other,
propagation of light is instantaneous; for then the waves will interfere
when we see a piece of artillery fired at constructively and will be bright at the
great distance, the flash reaches our eyes detector. Otherwise, there will be
without lapse of time; but the sound alternating patches of light and dark
reaches the ear only after a noticeable areas called interference fringes. The
interval. Galileo in Two New Sciences, wavelength of the radiation in the
published in Leyden in 1638, proposed that interferometer can be determined from: ? =
the question might be settled in true 2 L/N -- L is the length increase of one
scientific fashion by an experiment over a path, N is the number of maxima observed
number of miles using lanterns, during the increase.
telescopes, and shutters. www.contilab.com/ligo.
41667 Lantern Experiment. A. B. Human 141887 Michelson-Morley Experiment.
reaction times are approx. 0.2 sec and Theoretical implications of this result is
therefore, too slow to determine c with that the equations for the electromagnetic
any accuracy. Proved speed of light was field must by their very nature reflect
finite and showed that light travels at the indifference to the ethers motion.
least 10x faster than sound. The Accademia This implies that Maxwells equations must
del Cimento of Florence took Galileos remain invariant under the transformation
suggestion and made the first attempt to from one reference system to another.
actually measure the velocity of light. Michelson and Morley experiment produced a
Two people, A and B, with covered lanterns null result in regards to ether wind. From
went to the tops of hills about 1 mile Jack Meadows, The Great Scientists.
apart. First A uncovers his lantern. As 151891: Blondlots Parallel Wires.
soon as B sees A's light, he uncovers his Selected frequencies were transmitted
own lantern. Measure the time from when A along a pair of parallel wires and
uncovers his lantern until A sees B's reflected at the far end. This created a
light, then divide this time by twice the system of stationary waves with nodes and
distance between the hill tops. Therefore, antinodes spaced a regular intervals.
the speed of light would theoretically be Knowing the frequencies and the distances
c = (2D)/t. Approx one mile. between nodes, the speed of the radiation
5Longitude and Jupiters Moons. could be determined. Blondlots determined
Thousands of men were lost at sea because c = 297,600 km/sec.
there was no accurate way of determining www.ph.unimelb.edu.au/staffresources/lecde
longitude at sea. Galileo proposed using /ei2.htm.
an eclipse of one of Jupiters moons to 16L. Essens 1950 Microwave Cavity
determine the difference in longitude Resonator. Essen used radiation to produce
between two places. Olaf Roemer took up standing waves in a closed hollow metal
the task of using Jupiters moons to cylinder He produced radiation with
determine longitude. resonant frequencies of 9.5 GHz, 9 GHz,
astronomy.swin.edu.au/~pbourke/geometry/sp and 6 GHz wavelength of the radiation in
ere/. free space is determined by:(1/?)2 =
61676: First Hard Evidence For the (?/D)2 + (n/2L)2 D is the diameter of the
Finite Speed of Light. Olaf Roemer noticed cylinder L is the length n is the # of
variations in the eclipse times of Io, the half-wavelengths inside the cavity ? is
innermost moon of Jupiter. When the Earth obtained from solving wave equations Essen
moved away from Jupiter, the moon appeared used this method to determine c c =
to stay behind the planet 22 minutes 299,792.5 ? 3 km/s using c = ?? ? is the
longer than when the Earth was moving resonant frequency ? is the wavelength in
towards Jupiter. He used the equation: c = free space.
(d1 - d2)/(t1 - t2) t2 = time of eclipse 17Froomes 1958 Four-Horn Microwave
when the Earth is moving toward Jupiter t1 Interferometer. Froome generated 72 GHz
= time of eclipse when the Earth is moving radiation and sent it through his
away d2 = distance the Earth moves during interferometer. Radiation divided into two
t2. d1 = distance the Earth travels during beams, sent through two identical
time t1, Roemer determined that c = 2.1 x waveguides and out to two receivers on a
108 m/s. One third to slow because he was movable cart. Moving the receiver changed
using inaccurate information on the radius the path lengths of the two beams and
of the Earth's orbit. Io. Eclipse lasts caused interference in the detector. Every
longer than it should. Eclipse is shorter half-wave displacement in receiver, showed
than it should be. constructive interference. He determined
71728 Bradley and Stellar Aberration. the free space wavelength (?) of the
The stellar aberration is approximately radiation by: N ?/2 = ?z + A(1/z1 - 1/z2)
the ratio of the speed the earth orbits N is the number of interference minima A
the sun to the speed of light. Stellar is a constant ?z = z1 - z2 is the
aberrations cause apparent position of displacement of the cart. He calculated c
stars to change due to motion of Earth = 299,792.5 ? 0.3 km/s.
around sun. Bradley used stellar 181983 Breakthrough by Boulder Group:
aberration to calculate the speed of light Meter Redefined. Signals synthesized at
by knowing: speed of the earth around the progressively higher and higher
sun. the stellar aberration angle. His frequencies using harmonics generation and
independent confirmation, after 53 years mixing methods to lock the frequency of a
of struggle, finally absolutely ended the nearby oscillator or laser to the
opposition to a finite value for the speed frequency of this synthesized signal.
of light He calculated speed of light in a Photodiodes and metal-insulator-metal
vacuum as c = 301 000 km/s. diodes used for harmonic generation A
8Fizeaus 1849 Cogwheel Experiment. frequency chain was constructed linking a
Highlights of Fizeaus experiment: used a microwave output of the cesium frequency
slit to produce a narrow beam of light so the group could directly measure the
light travels through the spaces of a frequency of a helium-neon laser
cogwheel reflecst off of a mirror he stabilized against the 3.39 m transition
adjusted the rotational speed of the of methane. Resulted in a reduction in the
cogwheel until the light passes through uncertainty of speed of light by a factor
the next space on the wheel. c can be of 100 Formed basis for a new definition
calculated using the following: c = (2D * of the meter based on the speed of light.
v)/d D = distance between the wheel and The meter is the length of the path
the mirror v = the velocity of the wheel d traveled by light in a vacuum during the
= the distance between spaces on the wheel time interval of 1/299 792 458 of a
Using this method , Fizeau determined that second.. Led to the development of high
c = 3.15 x 108 m/s. resolution spectroscopic methods.
9Fizeaus 1851 Water Experiment. 19Historical Accuracy of speed of light.
Mirrors send a beam of light along two 20Classroom Application: Microwaving
different paths through moving water. One Marshmallows. Without rotating trays and
of the paths is in the same direction as reflecting fan, microwave ovens cook
the vw, other path was opposed to the vw. unevenly. A pattern of standing waves
When the two paths are looked at together forms inside the oven chamber. Creates an
they produce interference patterns. Speed array of hotspots throughout the oven's
of light through medium is determined from volume. An operating frequency of 2450 MHz
these patterns. Velocity of light in a produces a wavelength of 12.2cm. Hotspots
medium is c/n, where n is the index of should be at halfwave points, or
refraction. Proved Fresnel's prediction approximately every 6 cm, but in a complex
that if the medium was moving an observer 3D pattern. After about one minute on low
would measure the speed of light to be: power, a one layer sheet of small
v(light) = (c/n) + vmed(1-1/n2) If n=1, as marshmallows should have melt spots that
in a vacuum, the velocity remains resemble the pattern behind this text.
unchanged. Leads to the invariance of the 21Conclusion. Why would so many
c in different reference frames, a very scientists throughout the last four
important fact in relativity. centuries spend so much of their careers
10Maxwells 1865 Theoretical Conclusion. to make an accurate measurement of the
These equations have been tested for well speed of light? A small error in c causes
over a century now, and as far as we know, an enormous error in distance measurements
they are correct and complete. Their most to stars. Einstein's theory of relativity
spectacular prediction is that changing would not be possible without first
electric and magnetic fields can produce discovering that c is invariant in
each other by propagating as waves through different reference frames. These
space. Maxwell's equations predict that experiments eventually led to the
these waves should travel at a speed which redefinition of the meter in 1983.
just happens to be the speed of light. He 22Bibliography. Fishbane, P., S.
used the following equation to quantify Gasiorowitz, and S. Thornton. Physics for
the speed of light: Maxwell's theory held Scientists and Engineers. New Jersey:
that light is an electromagnetic Prentice Hall, 1993. Froome, K., and L.
oscillation, as are radio waves, Essen. The Velocity of Light and Radio
microwaves, infrared waves, X-rays, and Waves. London: Academic Press, 1969.
gamma rays. Halliday, D., R. Resnick, and J. Walker.
11Foucaults Method Introduced in 1875. Fundamentals of Physics. New York: John
Leon Foucault bounced light from a Wiley & Sons, 1993. Michelson, A.
rotating mirror on to a stationary curved Experimental Determination of the Velocity
mirror. This light is then reflected off of Light. Minneapolis: Lund Press, 1964.
this mirror back to the rotating mirror. Mulligan, J. Introductory College Physics.
Light is then deflected by a partially New York: McGraw-Hill Book Co., 1985.
silvered mirror to a point where it can Resnick, R., and D. Halliday. Basic
easily be observed. As the mirror is Concepts of Relativity. New York:
rotated, the light beam will focus at some MacMillan Publishing Company, 1992.
displacement from s in the figure. By Serway, R.A., and Faughn J.S.. College
measuring this displacement, c can be Physics. Florida: Harcourt,Brace& Co.,
determined from Foucaults equation: c = 1999 Sobel, D. and Andrewes, W.J., The
(4AD2?)/((A + B)?s) D is the distance from Illustrated Longitude. New York: Walker
the rotating mirror to the fixed mirror, A Publishing, 1998 Sullivan, D.B., Speed of
is the distance from L2 and L1, minus the Light From Direct frequency and Wavelength
focal length B is the L2 and the rotating Measurements. Matts Article he gave me on
mirror ? is the rotational velocity of the 7/22.
History of the Speed of Light ( c ).ppt
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c

History of the Speed of Light ( c )

History of the Speed of Light ( c )

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