13 DVO measurement of light velocity.ppt

7/23/2019 13 DVO measurement of light velocity.ppt

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Experiment done by French

physicist Armand Fizeau

measured speed of light In 1849


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3 !"

#otating tooth

$heel

slot

In 1849% French physicist ArmandFizeau measured speed of light

E

BC

D A

Experiment

set up


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&lotted $heel


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3 !"

#otating tooth

$heel

'eam of light is focused through

lens E ( falls on partial mirror )A*

slot

A

E


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3 !"

#otating tooth$heel

slot

After reflection from mirror A it

passes through slot in rotating

tooth $heelA


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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


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3 !"

#otating tooth

$heel

slot

After reflection from mirror - it

tra+els same path bac, ( enter

eye through partial mirror A

A

A


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/bser+ations ( calculations


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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


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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


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ime reuired for light to tra+el :; !" 2 time

reuired by $heel to rotate by angle


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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


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5 2 #otations < sec%.2 +elocity

of light

5umber of

teeth 2 14

685

:;.

2

:; x 568

. 2'y measuring 5

$e can calculate .


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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


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Another experiment

ha+ing more accuracy>?sing #otating mirror $ith

lesser


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A beam of light bounces between a rotating mirror &

a fixed mirror and back to the rotating mirror for a

total distance 2D,

- !"


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By the time light returns back to mirror in 2D / C secs

(where C is elocity of light! mirror will rotate

through some angle"

- !"


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#his will reflect light by $from original %ath"

- !"


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For different +alues of ,no$n angle % measure

#0" of mirror at $hich light becomes +isible


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.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


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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


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#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"


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#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"


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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.html


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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_apparatus


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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


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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


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/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


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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


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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 ==

13 DVO measurement of light velocity.ppt

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Transcript of 13 DVO measurement of light velocity.ppt