User:Garrett E. McMath/Notebook/Junior Lab/2008/10/27

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Plank's Lab

Photoelectric effect




We will be following the Gold's Lab manual's expirement for Plank's Constant


Experiment 1 A

White with Yellow Filter:

100% .797V 6.06s

100% .797V 6.34s

100% .797V 6.83s

80% .797V 9.13s

80% .797V 9.22s

80% .797V 9.44s

60% .797V 12.21s

60% .797V 13.28s

60% .797V 11.09s

40% .797V 16.75s

40% .797V 14.88s

40% .797V 15.88s

20% .797V 26.97s

20% .797V 26.09s

20% .797V 29.96s

Green Light Green Filter:

100% .847V 14.16s

100% .847V 13.59s

100% .847V 14.78s

80% .847V 17.75s

80% .847V 18.34s

80% .847V 19.31s

60% .847V 30.07s

60% .847V 27.88s

60% .847V 29.59s

40% .847V 35.41s

40% .847V 35.34s

40% .847V 34.88s

20% .847V 53.28s

20% .847V 61.47s

20% .847V 58.12s

Experiment 1 B

Trial 1 First Order:

  • Yellow: .717V
  • Green: .847V
  • Blue: 1.502V
  • Violet: 1.725V
  • UltraViolet: 2.077V

Trial 2 First Order:

  • Yellow: .714V
  • Green: .853V
  • Blue: 1.500V
  • Violet: 1.751V
  • UltraViolet: 2.078V

Trial 1 Second Order:

  • Yellow: .731V
  • Green: 1.269V
  • Blue: 1.519V
  • Violet: 1.730V
  • Ultra Violet: 2.071V

Trial 2 Second Order:

  • Yellow:.738V
  • Green:1.274V
  • Blue:1.520V
  • Violet:1.729V
  • Ultra Violet: 2.067V

Second Day Data, Experiment 1 B Cont.

1st order:

  • Yellow: .719
  • Green: .857
  • Blue: 1.510
  • Violet: 1.735
  • Ultra Violet: 2.075

Accepted Values

  • Work function: 1.36(08)eV
  • Plank's Constant: 4.13566733(10)E^-15eV*s

Accepted values of Mercury spetra

Yellow Green Blue Violet Ultra-Violet


5.18672E14 5.48996E14 6.87858E14 7.40858E14 8.20264E14
Wavelength(nm) 578 546.074 435.835 404.656 365.483

Sources of Error

  • Line Width:The rails that the focusing glass slid along were not long enough to accuratly focus the spectral lines so there is a high possiblity of overlapping spetral lines and or ambient light making it to the aperature thus skewing the data
  • Second Order Lines:While taking data we noticed a substantial difference in the stopping potential of the green spretral line between first and second order, we surmised that a possible reason for this would be non visible spetral lines of the first order overlapping the visible green line in the second order. Due to this theory we threw out our second oreder data as possibly corrupt.SJK 15:12, 16 November 2008 (EST)
    15:12, 16 November 2008 (EST)
    yup! take a look at Darrel's lab for how they solved this problem
  • Measurement:The measurement of the stopping potential with the multimeter creates the obvious error of slight charge loss durring the measurement due to non infinite resistance in the multimeter, this would be a fairly easy error to correct for by simply knowing the charge loss which I imagine could be found in the multimeter manual.
  • Discharge Button:As some cruel joke the makers of this apperatus chose to put the discharge button on the receiver of the light so that it was nearly impossible to push the button without slightly moving the aperture that the light was going through. I definatly think the button should have been attached by a chord to the receiver (like a jeopardy buzzer) (Steve Koch:Ha! Good analogy).

Data Analysis

Analysis performed in Excel, please open attached file to view data analysis 


Using the stopping potential averages of all the first order trials and graphing them vs. the frequencies of light associated with those stopping potentials we determined a best fit line whose slope is Planck's constant and whose y intercept is the work function.

  • Planck's Constant= 4.54234E-15 eV*s with an uncertainty of 5.13689E-17 eV*s which when compared to the accepted value of 4.13566733(10)E-15 eV*s gave a percent error of 9.38%
  • Work Function= -1.63573557 eV with an uncertainty of .034576054 eVwhich when compared to the accepted value of -1.36(08) eV gave a percent error of 20.27%


Lab Summary