Physics307L F09:People/sosa/planksconstant

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Photoelectric effect.svg.png Plank's Constant Report.pngMain project page
SJK Incomplete Feedback Notice
Incomplete Feedback Notice
My feedback is incomplete on this page for two reasons. First, the value of the feedback to the students is low, given that the course is over. Second, I'm running out of time to finish grading!

SJK 15:34, 17 December 2008 (EST)
15:34, 17 December 2008 (EST)
Also check Manuel's notebook for some comments.

Plank's Constant


Since the development of quantum mechanics in the early 20th century, the accurate determination of Plank's constant has been extremely important for accurate measurements. In experiment 1 (The Photon Theory of Light) we are going to demonstrate how the energy of electrons ejected when hit by photons only depends on frequency and not on intensity as predicted by the classical theories. In the second part of the experiment we will measure the constant of proportionality that is related to the kinetic energy of the electrons and the work function of the metal.

Plank's Constant Notes

Partner: Manuel Franco Jr.

Results and Analysis

Even though we are going to take some more data, I think it is convenient to do some analysis now so when the new data comes in, we can just plug in.

Experiment #1 (The Photon Theory of Light)

Analysis for part #1 File:Plank's Contant Part 1-1.xls

Green Line with Green Filter

  • Average maxV:0.8821 V
  • STD:0.00083666
  • SEM:0.000374166

Yellow Line with Yellow Filter

  • Average maxV:0.8821 V
  • STD:0.00083666
  • SEM:0.000374166


  • Average maxV:0.8821 V
  • STD:0.00083666
  • SEM:0.000374166

The objectives of this assignment were 2. To see how the charge time depends and intensity and to prove that the voltage does not vary with varying intensity. For the first obajective the results are more or less consistet. We can see that the three graphs shown display a smooth falling curve. As they should since the charge time is a function of the intensity. For the second objetive, sometimes the graphs display some variations on the order of 10E-3 volts. But I think these are tolarable variations since, as we could see, the voltmeter would fluctuate a lot even if our hands got close. So I think overall the fact that the energy of the electrons ejected from the metal does not depend on the intensity of the light is proved.

Experiment #2 Determination of h.

Actual Plank constant:(4.13)E-15 eV*s

Measured h:(3.72±0.16)E-15 eV*s

Percent Error:9.92%

Actual work constant:1.36(8) eV

Measured W0=(1.66±0.01)V

Percent Error:22.05%

SJK 15:31, 17 December 2008 (EST)
15:31, 17 December 2008 (EST)
Yeah, I did not understand your changing voltage problem either. You also had the "green 2nd order problem." The 1st and 2nd order are very inconsistent with each other, and thus a weighted average is not appropriate, but it's good you learned how to implement it, and good that you acknowledged Arianna's help.

I couldn't find your summary.

I actually was a bit surprised by these results. I did not expect them to be close to the actual values, since the voltmeter went a bit crazy on us after a couple of measurments reducing the voltage previously displayed. Of course voltmeters do not go crazy, so there must have some reason as to why the voltage started to decrease. Maybe some charge got trapped? I not quite sure. But we decided to carry on and make the measurments anyway.


I used Ariannas Excel analysis to guide me through my analysis.