Physics307L F09:People/Lancaster/Notebook/071001

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Day 2 of Speed of light

--Michael T. Lancaster 16:45, 1 October 2007 (EDT)


Measurements

The PMT value of 800 mV +/- .008 mV has been maintained. In the last measurement set the stick was pushed in. This time the stick will be pulled out, leading at least hopefully to larger voltages from the TAC as distance from the LED to the PMT is increased.

First run (pulling out)


   Voltage (V)              Distance (cm)              Place mark on meter stick
  
  4.72 +/- .04                   0                                60                           
  4.84 +/- .04                   6                                54                       
  4.80 +/- .04                   12                               48                    
  4.88 +/- .04                   18                               42                        
  4.92 +/- .04                   24                               36                 
  4.92 +/- .04                   30                               30                       
  4.96 +/- .04                   36                               24                    
  5.00 +/- .04                   42                               18                  
  5.04 +/- .04                   48                               12                       
  5.04 +/- .04                   54                               6               
                                                                       

--Michael T. Lancaster 19:09, 1 October 2007 (EDT)

The initial voltages are different because of a small voltage offset to make it easier to read. The O-scope has limited digital resolution that manifests as steps in the available numerical values. I represented these in the errors that I put on each entry. With Dr. Koch's help I set the O-scope so the TAC reading was mostly of the screen and used the measure function to determine its value. This improved the resolution of the reading by a factor of two, changing it from .04 to .02. This allowed me to measure much more accurately and also have more valid data points along the same range of values (~60 cm).

Second run (pushing in)


   Voltage (V)              Distance (cm)             Place on meter stick
  
  5.12 +/- .02                   0                                10
  5.14 +/- .02                   2                                12
  5.12 +/- .02                   4                                14
  5.12 +/- .02                   6                                16
  5.10 +/- .02                   8                                18
  5.08 +/- .02                   10                               20
  5.06 +/- .02                   12                               22
  5.06 +/- .02                   14                               24
  5.04 +/- .02                   16                               26
  5.02 +/- .02                   18                               28
  5.04 +/- .02                   20                               30
  5.00 +/- .02                   22                               32
  Tape in the way for stick marker 34 
  4.96 +/- .02                   26                               36
  4.96 +/- .02                   28                               38
  4.92 +/- .02                   30                               40
  4.92 +/- .02                   32                               42
  4.90 +/- .02                   34                               44
  Tape in the way for stick marker 46
  4.86 +/- .02                   38                               48
  4.86 +/- .02                   40                               50
  4.84 +/- .02                   42                               52
  4.82 +/- .02                   44                               54
  4.82 +/- .02                   46                               56
  4.80 +/- .02                   48                               58
  4.80 +/- .02                   50                               60

Data Analysis and Report

With the enhanced resolution of the O-scope I was able to return a larger number of measurements in the same range.



Media:Speed of Light (ML).xls


Image:Speed of light(mike).JPG

--Michael T. Lancaster 16:13, 17 October 2007 (CDT)

The measurements of distance from the meter stick when aligned with the end of the cardboard tube have insignificant error associated with them. The TAC measurements are subject to the digital step size error of the o-scope. Since the step size is .02 volts I will make the assumption that the error is +/- .01 volts.

The mean voltage value is 4.97333

Relative error is .01/4.97333 = .002011 or .2011%

Image:SpL (mike).jpg

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