Post on 14-Feb-2018
7/23/2019 13 DVO measurement of light velocity.ppt
1/36
Experiment done by French
physicist Armand Fizeau
measured speed of light In 1849
7/23/2019 13 DVO measurement of light velocity.ppt
2/36
3 !"
#otating tooth
$heel
slot
In 1849% French physicist ArmandFizeau measured speed of light
E
BC
D A
Experiment
set up
7/23/2019 13 DVO measurement of light velocity.ppt
3/36
&lotted $heel
7/23/2019 13 DVO measurement of light velocity.ppt
4/36
3 !"
#otating tooth
$heel
'eam of light is focused through
lens E ( falls on partial mirror )A*
slot
A
E
7/23/2019 13 DVO measurement of light velocity.ppt
5/36
3 !"
#otating tooth$heel
slot
After reflection from mirror A it
passes through slot in rotating
tooth $heelA
7/23/2019 13 DVO measurement of light velocity.ppt
6/36
3 !"
#otating tooth
$heel
slot
It then goes through lens '% tra+els
3 ,m as parallel beam ( gets
focus on mirror - thru lens .
BC
D
7/23/2019 13 DVO measurement of light velocity.ppt
7/36
3 !"
#otating tooth
$heel
slot
After reflection from mirror - it
tra+els same path bac, ( enter
eye through partial mirror A
A
A
7/23/2019 13 DVO measurement of light velocity.ppt
8/36
/bser+ations ( calculations
7/23/2019 13 DVO measurement of light velocity.ppt
9/36
At lo$ #0" of $heel% the light beam returns
through the same opening through $hich it
$as transmitted #0& 2 rotation per sec
5umber of
teeth 2 16
7/23/2019 13 DVO measurement of light velocity.ppt
10/36
7As the #0" increases% the light is bloc,ed bythe $heel as it ad+anced half the distancebefore light returns 5ote the speed of $heel
#otation per sec
5umber of
teeth 2 16
7/23/2019 13 DVO measurement of light velocity.ppt
11/36
ime reuired for light to tra+el :; !" 2 time
reuired by $heel to rotate by angle
7/23/2019 13 DVO measurement of light velocity.ppt
12/36
5 2 "easured
re+olutions < sec
5umber of teeth 2142 3=;< 68
ime for rotation of o
68
5
2 &ecs
As .ircle is
di+ided in 68parts14 tooth (
14 slots
7/23/2019 13 DVO measurement of light velocity.ppt
13/36
5 2 #otations < sec%.2 +elocity
of light
5umber of
teeth 2 14
685
:;.
2
:; x 568
. 2'y measuring 5
$e can calculate .
7/23/2019 13 DVO measurement of light velocity.ppt
14/36
7 Further increasing #0&% the $heel ad+ances
to next slot and returned beam becomes
+isible through next slot his reading can
also be used to calculate .
5umber of
teeth 2 14
7/23/2019 13 DVO measurement of light velocity.ppt
15/36
7/23/2019 13 DVO measurement of light velocity.ppt
16/36
Another experiment
ha+ing more accuracy>?sing #otating mirror $ith
lesser
7/23/2019 13 DVO measurement of light velocity.ppt
17/36
A beam of light bounces between a rotating mirror &
a fixed mirror and back to the rotating mirror for a
total distance 2D,
- !"
7/23/2019 13 DVO measurement of light velocity.ppt
18/36
By the time light returns back to mirror in 2D / C secs
(where C is elocity of light! mirror will rotate
through some angle"
- !"
7/23/2019 13 DVO measurement of light velocity.ppt
19/36
#his will reflect light by $from original %ath"
- !"
7/23/2019 13 DVO measurement of light velocity.ppt
20/36
For different +alues of ,no$n angle % measure
#0" of mirror at $hich light becomes +isible
7/23/2019 13 DVO measurement of light velocity.ppt
21/36
7/23/2019 13 DVO measurement of light velocity.ppt
22/36
.alculations
7 In one rotation mirror rotates by 6;
7 If #0" of mirror is 5% in one sec mirror $illrotate =; x 6x 5 degrees7 5o$ mirror has rotated by angle
7/23/2019 13 DVO measurement of light velocity.ppt
23/36
A similar exp $as repeated to find effect of
+elocity of medium on +elocity of light It $s found
that light +elocity remained same
ater
7/23/2019 13 DVO measurement of light velocity.ppt
24/36
7/23/2019 13 DVO measurement of light velocity.ppt
25/36
#he basic techniue is to send a beam of on a %ath so that it bounces between a
rotating mirror, a fixed mirror and back to the rotating mirror for a total distance
2D, as shown in the aboe illustration" #he time of flight of the light on this %ath
im%lies that the rotating mirror will hae turned ery slightly between the two times
of arrial of the light" #his small rotation will deflect the beam of light through asmall angle ' from its original %ath, %roducing a measurable effect %ro%ortional to
the mirror and inersely %ro%ortional to the s%eed of light"
f the rotational freuency (reolutions %er unit time! of the mirror is gien by ),
then the deflection angle is gienby
D
cc
D
*!2(!2(2 ==
,
where the second factor angular freuency of
rotation and the last is the time to trael back and
forth between the mirrors"
7/23/2019 13 DVO measurement of light velocity.ppt
26/36
#he basic techniue is to send a beam of on a %ath so that it bounces between a
rotating mirror, a fixed mirror and back to the rotating mirror for a total distance
2D, as shown in the aboe illustration" #he time of flight of the light on this %ath
im%lies that the rotating mirror will hae turned ery slightly between the two times
of arrial of the light" #his small rotation will deflect the beam of light through asmall angle ' from its original %ath, %roducing a measurable effect %ro%ortional to
the mirror and inersely %ro%ortional to the s%eed of light"
f the rotational freuency (reolutions %er unit time! of the mirror is gien by ),
then the deflection angle is gienby
D
cc
D
*!2(!2(2 ==
,
where the second factor angular freuency of
rotation and the last is the time to trael back and
forth between the mirrors"
7/23/2019 13 DVO measurement of light velocity.ppt
27/36
7/23/2019 13 DVO measurement of light velocity.ppt
28/36
In 1849 French physicist Armand Fizeau de+eloped a de+ice ,no$n as the Fizeau $heel in
http://scienceworld.wolfram.com/biography/Fizeau.htmlhttp://scienceworld.wolfram.com/biography/Fizeau.html7/23/2019 13 DVO measurement of light velocity.ppt
29/36
FizeauBFoucault apparatus
In 1849% French physicistArmand Fizeau de+eloped a de+ice ,no$n as the Fizeau $heel in
order to measure the speed of light his instrument consists of a rotating toothed $heel
through $hich a beam of light is passed he light is then reflected by a distant mirror% $hich
reflects it bac, to the $heel hen the rotation speed is lo$% the light beam returns uic,ly
enough so as to pass through the same opening through $hich it $as transmitted As the
rotation speed increases% the light is bloc,ed because the $heel has ad+anced oneChalf the
distance bet$een openings Further increasing the speed% the $heel ad+ances the entiredistance bet$een openings% and the beam again passes through !no$ing all the dimensions
in+ol+ed and the speeds at $hich the light beam passed or didnDt pass% Fizeau could calculate
the speed of light
he apparatus $as subseuently impro+ed upon by FizeauDs contemporary ean Foucault%
$ho used a rotating polygonal mirror and a distant mirror As the light beam returned from its
path to the distant mirror% the rotating mirror had ad+anced slightly and the beam $as reflected
at a slight angle by a different face of the mirror !no$ing the deflection angle% the distance to
the fixed mirror% and the speed of rotation% he calculated the speed of lightto be 698%;;;%;;;
meters per second% +ery close to the currently accepted +alue
http://en.wikipedia.org/wiki/Fizeau%E2%80%93Foucault_apparatushttp://scienceworld.wolfram.com/biography/Fizeau.htmlhttp://scienceworld.wolfram.com/physics/SpeedofLight.htmlhttp://scienceworld.wolfram.com/physics/SpeedofLight.htmlhttp://scienceworld.wolfram.com/biography/Foucault.htmlhttp://scienceworld.wolfram.com/physics/SpeedofLight.htmlhttp://scienceworld.wolfram.com/physics/SpeedofLight.htmlhttp://scienceworld.wolfram.com/biography/Foucault.htmlhttp://scienceworld.wolfram.com/physics/SpeedofLight.htmlhttp://scienceworld.wolfram.com/physics/SpeedofLight.htmlhttp://scienceworld.wolfram.com/biography/Fizeau.htmlhttp://en.wikipedia.org/wiki/Fizeau%E2%80%93Foucault_apparatus7/23/2019 13 DVO measurement of light velocity.ppt
30/36
7/23/2019 13 DVO measurement of light velocity.ppt
31/36
For our setup% $e used a lens $ith a focal length of m% and set and* to be 1;m e set the distance - to be approximately 13m and -* to
be :m In order to obser+e the deflection of the beam% $e inserted a
thin to minimize internal reflections microscope slide beam splitter Gust
before the source /ur rotating mirror is based on a 'osch router motor%
$ith a pea, speed of 6:;;;rpm at 16;H A.
#otating mirror
7/23/2019 13 DVO measurement of light velocity.ppt
32/36
he FizeauFoucault apparatus18; Figure 1 $as designed by the French
physicists@ippolyte Fizeau and Jon Foucault for measuring the speed of light he
apparatus in+ol+es light reflecting off a rotating mirror% to$ard a stationary mirror
some 6; miles 3 ,ilometers a$ay As the rotating mirror $ill ha+e mo+ed slightly in
the time it ta,es for the light to bounce off the stationary mirror and return to therotating mirror% it $ill thus be deflected a$ay from the original source% by a small
angleK1L If the distance bet$een mirrors is h% the time bet$een the first and second
reflections on the rotating mirror is 6h
7/23/2019 13 DVO measurement of light velocity.ppt
33/36
/bser+ations>
7 At lo$ #0" of $heel% the light beam returns
through the same opening through $hich it $as
transmitted
7 As the #0" increases% the light is bloc,ed by
the $heel as it ad+anced oneChalf the distance
before light returns 5ote the speed of $heel
7 Further increasing #0"% the $heel ad+ancesto next slot and returned beam becomes
+isible through next slot
7/23/2019 13 DVO measurement of light velocity.ppt
34/36
7As the rotation speed increases% the light is
bloc,ed because the $heel has ad+anced oneC
half the distance bet$een openings
7 Further increasing the speed% the $heel
ad+ances the entire distance bet$een
openings% and the beam again passes through
7 !no$ing all the dimensions in+ol+ed and the
speeds at $hich the light beam passed or didnDtpass% Fizeau could calculate the speed of light
7
7/23/2019 13 DVO measurement of light velocity.ppt
35/36
7/23/2019 13 DVO measurement of light velocity.ppt
36/36
A beam of light bounces between a rotating mirror, a
fixed mirror and back to the rotating mirror for a total
distance 2D, #he rotating mirror will hae turned by
angle /2 by the time light returns back to mirror
(2D / C secs! "#his will reflect light by $from
original %ath" By measuring this angle we can
calculate elocity of lightf +- mirror is gien by v, then the deflection angle
is measured as
Dcc
D
*!2(!2(2 ==