User:Chad A McCoy/Notebook/Jr. Lab/2008/11/10

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SJK 18:09, 18 December 2008 (EST)
18:09, 18 December 2008 (EST)
Your oscilloscope method for assessing the burst time was very cool. You definitely win the "master of the oscilloscope" award for this semester...and I expect you to retain that title should anyone challenge you :)

Planck's Lab: 11/10/2008

  • For the fifth lab experiment, I have chosen to do the Planck lab, in which I am measuring the ratio h/e and from that the value of Planck's constant.
  • For materials, I am using a Tektronix TDS1002 Two Channel Digital Storage Oscilloscope, Pasco Scientific AP-9368 h/e apparatus, Wavetek 85XT True RMS Multimeter, and a Pasco Scientific OS-9286 Mercury light source.
  • To measure the values I am using the digital multimeter and an oscilloscope to measure the value of the stopping potential of the freed electrons due to the photoelectric effect.
  • See the lab manual for more info on the apparatus.
  • To prepare to begin taking data, I allowed the light source to heat up, and focused the beam on the center of the h/e apparatus.
  • Having done this, I rotated the apparatus about the coupling and found the ultraviolet beam of the first order.

Experiment #1

  • For this experiment I am measuring the amount of time required for the electrode to recharge after discharging the capacitor, in an attempt to determine the burst time for charging.
  • To do this I am setting the oscilloscope to run a single sequence, and after discharging, covering the opening such that at removal, the amount of charge will spike, and looking at the individual burst with the oscilloscope, I will be able to measure the burst time for the different level of intensity.
Charge time vs. Transmission percentage
Transmission % Burst Time Voltage V/t
20% 14.8ms 16.00ms 1.30V 1.30V
40% 10.8ms 10.0ms 1.24V 1.46V
60% 13.2ms 11.2ms 1.40V 1.58V
80% 8.0ms 5.6ms 1.34V 1.38V
100% 8.4ms 4.8ms 1.54V 1.30V


Charge time to full vs. Transmission percentage in ultraviolet and violet lines
Transmission % UV (2.4V) Violet (1.71V)
20% 58.1s 40.1s
40% 42.3s 39.89s
60% 23.25s 27.94s
80% 14.60s 15.13s
100% 8.35s 5.12s
Charge time to full vs. Transmission percentage in yellow and green lines
Transmission % Green(.840V) Yellow (.708V)
20% 29.97s 37.03s
40% 25.06s 34.16s
60% 14.72s 24.10s
80% 11.07s 14.67s
100% 8.56s 8.09s
  • To take these data sets I aligned the specific spectral line, and discharged the apparatus, starting a stopwatch at the time of discharge, and stopping it when it reached the max value.
  • Note: I used the max value at the max for the 20% so that the time would stop when all the data sets reached the same peak value.

Experiment #2

  • For this I am measuring Planck's constant from the value of the first and second order lines, by making a least-squares regression, of which the slope will be Planck's constant and the intercept will be the work function.
First order lines and measured Voltage
Color Voltage
Ultra Violet 2.075V 2.057V 1.993V
Violet 1.736V 1.718V 1.689V
Blue 1.502V 1.491V 1.474V
Green 0.845V 0.851V 0.835V
Yellow* 0.713V 0.716V 0.705V
Second order lines and measured Voltage
Color Voltage
Ultra Violet 2.043V 2.041V 2.046V
Violet 1.711V 1.706V 1.712V
Blue 1.503V 1.507V 1.506V
Green 1.251V 1.246V 1.248V
Yellow* 0.729V 0.733V 0.734V
  • I had to use the orange line as yellow, because the yellow line for mercury did not resolve, and mercury's "yellow" line is generally considered to be the double yellow-orange lines at 578 and 580 nanometers.
  • For the second order measurements, I used the spectra seen to the right of the first order, and measured the ultraviolet, then violet, ..., through the yellow, and then went back to the UV and took the second data set.