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The experiment of Fizeau



The experiment of Fizeau

When you are inter­ested in physics you must read “Unbe­liev­able”!

Fres­nel intro­duced the drag fac­tor to explain or rather to com­pen­sate for the fact that the earth seemed to be at rest in the ether. Obvi­ously they were look­ing for proof of the absolute ether. If there was no ether it would be inex­plic­a­ble how light, fields and forces like grav­ity, elec­tro­sta­tic and mag­netic fields could be prop­a­gated through space. The urge to prove the exis­tence of the absolute ether was immi­nent. With­out the ether phys­i­cal char­ac­ter­is­tics, like the trans­porta­tion of light in vac­uum, became incon­ceiv­able and mys­te­ri­ous. Prov­ing the exis­tence of Fresnel’s drag fac­tor was nec­es­sary. Demon­strat­ing the drag fac­tor was not easy because of the extreme veloc­ity of the speed of light with approx. 300,000 km/​s.

In 1851 Fizeau devised an exper­i­ment with unknown accu­racy that was able to mea­sure Fresnel’s assumed drag factor.

Fig­ure 6. The exper­i­ment of Fizeau.

The light of source is divided up into two beams. One beam goes with the flow of water and the other beam against the flow. When the light in the water is dragged the light trav­el­ing against the water flow will need more time to travel through the tubes than if the light goes with the flow. This is com­pa­ra­ble with the time dif­fer­ence a swim­mer needs to swim with or against the cur­rent. The dif­fi­culty here is that the speed of the “swim­mer” is so high that it takes him only 1/100,000,000 of a sec­ond to fin­ish. The dif­fer­ence between with or against the flow is even much smaller.

Light is vibra­tion with a very short wave­length. Vibra­tions are able to for­tify or tone down each other when they meet. The dif­fer­ence between extin­guish­ing and for­ti­fy­ing, a bright and a dark line in the inter­fer­ence pat­tern, is about 140 of a mil­lionth of a meter. The inter­fer­ence of light is char­ac­ter­ized by bright and dark stripes: the inter­fer­ence lines. The whole pic­ture of dark and light stripes is called the inter­fer­ence pattern.

The exper­i­ment of Fizeau is called an opti­cal inter­fer­om­e­ter and was devised to mea­sure very small dif­fer­ences in time or dis­tance. The drag coef­fi­cient of Fres­nel, , implies in the exper­i­ment of Fizeau a drag of inter­fer­ence lines (λ the wave­length of the light, v the flow speed of the water and L the length). For the deriva­tion of this for­mula see the next chap­ter. Fizeau reg­is­tered dur­ing his exper­i­ment a shift of δ=0.23 in the inter­fer­ence lines; which impli­cates a drag fac­tor f=0.48; the empir­i­cal value. The the­o­ret­i­cal value of the drag fac­tor is cal­cu­lated with the for­mu­lasand and is cal­cu­lated at f=0.43. So within an error of approx. 10%, the exper­i­ment of Fizeau con­firmed Fresnel’s drag fac­tor.

Next chap­ter: The exper­i­ment of Fizeau and the dragged ether

When you are interested in physics you must read “Unbelievable“!

Fresnel introduced the drag factor to explain or rather to compensate for the fact that the earth seemed to be at rest in the ether. Obviously they were looking for proof of the absolute ether. If there was no ether it would be inexplicable how light, fields and forces like gravity, electrostatic and magnetic fields could be propagated through space. The urge to prove the existence of the absolute ether was imminent. Without the ether physical characteristics, like the transportation of light in vacuum, became inconceivable and mysterious. Proving the existence of Fresnel’s drag factor was necessary. Demonstrating the drag factor was not easy because of the extreme velocity of the speed of light with approx. 300,000 km/s.

In 1851 Fizeau devised an experiment with unknown accuracy that was able to measure Fresnel’s assumed drag factor.

Figure 6.  The experiment of Fizeau. 

The light of source is divided up into two beams. One beam goes with the flow of water and the other beam against the flow. When the light in the water is dragged the light traveling against the water flow will need more time to travel through the tubes than if the light goes with the flow. This is comparable with the time difference a swimmer needs to swim with or against the current. The difficulty here is that the speed of the “swimmer” is so high that it takes him only 1/100,000,000 of a second to finish. The difference between with or against the flow is even much smaller.

Light is vibration with a very short wavelength. Vibrations are able to fortify or tone down each other when they meet. The difference between extinguishing and fortifying, a bright and a dark line in the interference pattern, is about 1/40 of a millionth of a meter. The interference of light is characterized by bright and dark stripes: the interference lines. The whole picture of dark and light stripes is called the interference pattern.

The experiment of Fizeau is called an optical interferometer and was devised to measure very small differences in time or distance. The drag coefficient of Fresnel, implies in the experiment of Fizeau a drag of  interference lines (λ the wavelength of the light, v the flow speed of the water and L the length). For the derivation of this formula see the next chapter. Fizeau registered during his experiment a shift of δ=0.23 in the interference lines; which implicates a drag factor f=0.48; the empirical value. The theoretical value of the drag factor is calculated with the formulasand and is calculated at f=0.43. So within an error of approx. 10%, the experiment of Fizeau confirmed Fresnel’s drag factor.

Next chapter: The experiment of Fizeau and the dragged ether

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