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# Speed of Light

Unit C Rahma & Artemis
by

on 16 April 2010

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#### Transcript of Speed of Light

Speed of light
By: Rahma & Artemis Ole Roemer
(1644-1710)

Ole Roemer was a Danish Astronomer
He was the first to make an attempt to mesure the speed of light
He studied the eclipses of Jupiter and observed that the times of the eclipses of the moons of Jupiter depend on the position of Jupiter and Earth.
He noted that whenever Earth was closer to the moons of Jupiter it sped up the process it takes for the eclipse to take place
Knowing this he deduced that it was due to the distance the light had to travel (more distance more time for eclipse)

He came up with the value 200 000km/s as the speed of light
He was in a much more technologically advanced time than Galilleo which made it a lot easier for him to calculate this amount.

Galileo Galilei
(1564-1642)

Often mentioned as being the first to attempt to determine the speed of light
Galileo managed to deduce that light moves 10 times faster than sound
He was able to deduce this by having two people stand on distant hills with covered lanterns.
Essentially the point of the experiment was to have one person uncover their lantern and as soon as person #2 saw the light they would uncover their lantern.
He was looking to see if the time would have lengthened.

Christiaan Huygens

Came up with laws of reflection and refraction (but was later disputed and corrected by Fresnel)
he also tried to calculate the speed of light using Roemer's data but misinterpreted Roemer's value of 22 minutes as the time in which light travels the diameter of Earth

Sources used.
http://www.speed-light.info/measure/roemer.htm
http://www.speed-light.info/
http://maxwell.byu.edu/~spencerr/phys442/node4.html
http://galileoandeinstein.physics.virginia.edu/lectures/spedlite.html
http://www.speed-light.info/measurement.htm

Foucault and Fizeau
Both french physicist that lived in 1800
Fizeau
Fizeau built an apparatus that he also used to mesure the speed of light
the apparatus he built shone light between the teeth of a rapidly rotating toothed wheel.
A mirror that was a certain distance away reflected the beam back through the same gap between the teeth of the wheel.
He used the time it took for it to turn and the period
he was already aware of the distance the light travelled thus enabling him to use the simple formula v= d/t to mesure the speed
He mesure the speed of light to be 313,300 Km/s
Foucault

Foucaults apparatus was based on Fizeau
The apparatus consisted of a rotating mirror and a stationary mirror
He tried to calculate the amount of time it would take for the light from the rotating mirror to hit the stationary mirror and back on to the rotating mirror
But the first mirror was rotating, the light from the rotating mirror finally bounced back at an angle slightly different from the angle it initially hit the mirror (the reflection angle)
By measuring this angle, it was possible to measure the speed of the light.
Foucault mesure the speed of light to be 299,796 Km/s Foucaults Apparatus Albert Michelson
First man to receive nobel prize in Sciences (1907)
As early as 1877 Michelson began his work trying to refine Foucaults Apparatus to mesure the speed of light
he used improved optics and a longer baseline and used the best equipment available in his day
doing this he managed to mesure a more accurate mesurement for the speed of light which was 299,796 km/second

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