User:David E. Sosa/Notebook/2008/09/17/Summary
Speed of Light Lab | <html><img src="/images/9/94/Report.png" border="0" /></html> Notebook |
SJK 23:24, 6 October 2008 (EDT)
ObjectiveThe objective of this experiment is to determine the speed of light with the greatest possible accuracy. Lab Partner: Manuel Franco EquipmentSJK 02:47, 6 October 2008 (EDT)
Some images of the materials used
Setup and ConnectionsWhen we arrived everything was already setup by the Lab prior to us, but we still had to review the equipment and wires to check if they were in the correct place. We were aided by Dr. Koch and the TA Aram, but also by Dr. Caves' Lab Manual, Section 10.
ProcedureAfter checking everything was set up correctly, we turned on the TAC, both DC power supplies, and the oscilloscope. So as instructed by the lab manual, we set the TAC power supply to about 1800 V to 2000 V like the manual suggests. We decide set the TAC power supply at 1990 V, and the other DC power supply to 150 V. We didn' get any graph on the oscilloscope. After trying to determine the reason for this we decided to ask for help. With help from Koch, we figured out that the DC power supply connectted to the LED was set too low, and that our DSO was out of range. So we set the DC power to 170 V (+/- 1 V), and ranged the DSO. Finally, we obtained the two graphs necessary to record data, as shown in Photo 2. Time walk was a new concept we had to learn for this experiment. The speed of light travels approximately a foot per nanosecond; so the instant we turned on the equipment and the LED emitted that pulse, light had to travel several feet to light up the LED. That delay in light would provide the wrong data. The delay would help us make a reference to how light was moving. As for the TAC, it had to be trigger at a fixed voltage due to the polarization in the PMT and LED. The lab manual goes more in to detail over this process. As we moved the LED and PMT we change the distance between them, and we measured the voltage in which we get the time from that. Whether if we bring the LED closer to the PMT, or if we pull the LED away from the PMT the speed of light is constant. With this data we can make distance and time graph. With that we can obtain a slope or velocity, hence our measurement of the speed of light. Data TakenDC Power supply: 170 V (-/+ 1 V) on all measurements 1st Measurement
1.) 150 cm 2.56 V 2.) 140 cm 3.48 V 3.) 120 cm 3.68 V 4.) 100 cm 3.36 V 5.) 80 cm 3.12 V 6.) 60 cm 2.69 V 7.) 50 cm 2.12 V 2nd Measurment
1.) 60 cm 2.10 V (+/- 0.04 V) 2.) 50 cm 2.04 V (+/- 0.04 V) 3.) 40 cm 2.02 V (+/- 0.04 V) 4.) 30 cm Same as above 5.) 20 cm 1.95 V (+/- 0.04 V) 6.) 10 cm 1.84 V (+/- 0.04 V) 3rd Measurment (BEST DATA)
1.) 160 cm 3.00 V (-/+ 0.04 V) 2.) 150 cm 2.94 V (-/+ 0.04 V) 3.) 140 cm 2.90 V (-/+ 0.04 V) 4.) 130 cm 2.87 V (-/+ 0.04 V) 5.) 120 cm 2.82 V (-/+ 0.04 V) 6.) 110 cm 2.78 V (-/+ 0.04 V) 7.) 100 cm 2.70 V (-/+ 0.04 V) 8.) 90 cm 2.66 V (-/+ 0.04 V) 9.) 80 cm 2.54 V (-/+ 0.04 V) 10.) 70 cm 2.52 V (-/+ 0.04 V) 11.) 60 cm 2.46 V (-/+ 0.04 V) 12.) 50 cm 2.38 V (-/+ 0.04 V) 4th MeasurementSome Measurements with time delay
1)130 cm 2.38 V (-/+ 0.04 V) 2)120 cm 2.34 V (-/+ 0.04 V) 3)110 cm 2.22 V (-/+ 0.04 V) 4)100 cm 2.14 V (-/+ 0.04 V) 5)80 cm 2.04 V (-/+ 0.04 V) Results and Data AnalysisMeasurements 1,2, and 4 were ignored due to trial and error. Measurement 3 was most accurate out of all data accumulated. All our data is in this spread sheet. We followed Jessy's format to plot and analyze the data.The slope, or measurement for the speed of light is 352261684.3 m/s. SJK 23:11, 6 October 2008 (EDT)ConclusionSJK 22:48, 6 October 2008 (EDT) Our result was ~17% deviated from the accepted value. We might have obtained better results if we had taken more measurements to compare. Unfortunately due to lack of time we weren't able to. Overall I think it is a hard laboratory. Many new concepts are introduced, but I also think it is really important. How many people can say they have measured the speed of light? One of the reasons I want to become a scientist is to check things myself, and not be told that X or Y is true just because someone said it a long time ago.SJK 22:46, 6 October 2008 (EDT)References |