The Speed of Light: Historical Perspective and Experimental Findings
The Speed of Light: Historical Perspective and Experimental Findings
The Speed of Light: Historical Perspective and Experimental Findings
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TRENT SCARBOROUGH AND BEN WILLIAMSON<br />
splitter. From the microscope on the beam splitter, the spectral<br />
field could be observed, <strong>and</strong> thus the image point (See<br />
Appendix 3 for diagrams).<br />
After meticulously aligning the equipment, we were ready to<br />
begin. <strong>The</strong> emission filtering <strong>of</strong> the beam splitter produced the<br />
unique pattern <strong>of</strong> a small, sharp, bright dot (our image point)<br />
adjacent to a bright <strong>and</strong> equally sharp b<strong>and</strong>, quite separate from<br />
the rest <strong>of</strong> the apparent emission in the spectral field. <strong>The</strong> rotating<br />
mirror was activated <strong>and</strong> the speed was increased to<br />
approximately 600 rotations per second (rev/s) to allow the<br />
motor to warm up. After three minutes, the speed was increased<br />
to 1 000 rev/s <strong>and</strong> then the speed to its maximum velocity,<br />
approximately 1 500 rev/s.<br />
As the mirror rotated continuously at high velocity, a laser<br />
pulse was generated which resulted in a strange phenomenon:<br />
the incident light strikes the rotating mirror at a different angle<br />
than the reflected light thus, allowing measurable displacement<br />
with the image point to be seen. <strong>The</strong> small dot in the spectral<br />
field was displaced <strong>and</strong> measured with a micrometer. This<br />
process was repeated at least twice for each direction (clockwise<br />
<strong>and</strong> counterclockwise), <strong>and</strong> the results were tabulated.<br />
Using these results, we were able to determine a value for the<br />
speed <strong>of</strong> light <strong>of</strong> 2.992 x 10 8 m/s for the speed <strong>of</strong> light in air. 12<br />
<strong>The</strong> value found is 0.198% below the currently accepted value.<br />
Foucault’s original experiment produced a value <strong>of</strong> the speed <strong>of</strong><br />
light, c = 2.99792 x 10 8 m/s, approximately 1% lower than the<br />
modern value. It should be noted that in this experiment the<br />
speed <strong>of</strong> light is measured in air, the value <strong>of</strong> which mathematically<br />
should be approximately 0.03% lower. <strong>The</strong> greater precision<br />
in our results stems from several factors, almost all <strong>of</strong> them<br />
due to our equipment. We were able to use a laser light source,<br />
where Foucault had to use st<strong>and</strong>ard light bulb. We were also<br />
able to electronically control <strong>and</strong> measure precisely our rotation<br />
speed, whereas, Foucault did not have the use <strong>of</strong> any modern<br />
electronics.<br />
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