Physics307L:People/Archer

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Oscilloscope Lab

^{SJK 03:27, 17 September 2008 (EDT)}

03:27, 17 September 2008 (EDT)
Overall, very good lab! Except for a couple things missing (noted on the raw data page), your notes are very details and your summary table is great.

The raw data from the lab is here.

In summary, I measured the peak-to-peak voltage and period of multiple sine waves of three different amplitudes the peak-to-peak voltage and period of a sine wave with a large DC offset, as well as the fall time of a DC Voltage read through AC coupling, measured by placing cursors at the peak of the function and at the 90% decay point of the function, as well as automatic calculation in the oscilloscope. I measured everything else by visual inspection, cursor inspection, and automatic calculation in the oscilloscope.

^{SJK 03:12, 17 September 2008 (EDT)}

03:12, 17 September 2008 (EDT)
This table is a nice and succinct way to report your results...glad you decided to use it! It would probably be more readable if you combined the error with the measurements (e.g. "value ± error")...we'll talk about this during lecture soon.

I also think there are some typos in your error values for some entries (e.g. 5 +/- 5)

MEASUREMENTS	Visual	Cursors	Calculate	ERROR	Visual	Cursors	Calculate
Pk-Pk 200 Hz	500 mV	508 mV	504~508 mV		100 mV	16 mV	1 mV
Period 200 Hz	5 ms	5.2 ms	5.128~5.144 ms		5 ms	0.8 ms	0.001 ms
Pk-Pk Hi-Amp	2200 mV	2220 mV	2180~2200 mV		200 mV	80 mV	10 mV
Period Hi-Amp	5 ms	5.2 ms	5.110~5150 mV		5 ms	0.8 ms	0.001 ms
Pk-Pk Lo-Amp	60 mV	59.2 mV	60.0~63.2 mV		20 mV	3.2 mV	0.1 mV
Period Lo-Amp	5 ms	5.2 ms	5.110~5.170 ms		5 ms	0.8 ms	0.001 ms
Pk-Pk Offset	900 mV	880 mV	864~872 mV		100 mV	32 mV	1 mV
Period Offset	5 ms	5.2 ms	5.130~5.140 ms		5 ms	0.8 ms	0.001 ms
Fall Time	n/a	58 ms	49.40~56.00 ms		n/a	4 ms	0.01 ms
Time Constant	n/a	26.3 ms	24.0 ms		n/a	1.8 ms	1.5 ms

I am satisfied with this result, since nothing seems to be too unexpected. I would attribute the fluctuations to random error. If I had more time, I might examine Fourier transform phenomena in the wave functions.

I am still confused by the nature of capacitive coupling. ^{SJK 03:10, 17 September 2008 (EDT)}

03:10, 17 September 2008 (EDT)
we can talk about this some more when you'd like

I did not explore anything outside of the lab parameters. I have no suggestions for this lab. ^{SJK 03:26, 17 September 2008 (EDT)}

03:26, 17 September 2008 (EDT)
This was a pretty straightforward lab, so it's fine not to have comments. However, this kind of thinking ("what would I do if I had more time to take better data?") is good thinking to practice, and you'll want to put some more effort into this in the future labs.

Planck's Constant Lab

The raw data for the lab can be found on the following pages:9/15/08 and 9/29/08.

In summary, I measured the stopping potentials (taken to be the maximum potentials measured) in a photodiode of multiple wavelengths of light diffracted from a mercury lamp at multiple levels of intensity, as well as the time taken to achieve this stopping potential for some of these wavelengths.

For Photon Theory Part A,

Green Wavelength	100% Intensity	80% Intensity	60% Intensity	40% Intensity	20% Intensity
Stopping Potential	0.886~0.887 V	0.886~0.887 V	0.875 V	0.873 V	0.871 V
Mean Time to Reset	48.20 s	58.64 s	38.00 s	46.89 s	91.08 s
Standard Deviation	5.94 s	3.82 s	1.90 s	0.34 s	8.50 s
Number of Measurements	5	5	3	3	3

For Photon Theory Part B,

First Order	Yellow	Green	Blue	Violet	Ultraviolet
Mean Stopping Potential	0.746 V	0.885 V	1.526 V	1.752 V	2.057 V
Standard Deviation	0.005 V	0.007 V	0.009 V	0.016 V	0.016 V
Number of Measurements	3	3	3	3	3

Passing different intensities of same-colored light has very little effect on stopping potential and thus very little effect on photon energy; the charging time therefore should not be affected.

Longer wavelengths of light have lower stopping potentials, while higher wavelengths have higher potentials, by extension, shorter wavelengths have higher energies.

This lab supports a photon-based model of light, since the wavelength (rather than the intensity) has the greatest effect on stopping potential by far.

The slight drop in stopping potential is possibly due to the physical limitations of the photodiode used to capture wavelengths, which may not function properly for low intensities of light.

For Determination of Planck's Constant,

Second Order	Yellow	Green	Blue	Violet	Ultraviolet
Mean Stopping Potential	0.731 V	1.296 V	1.544 V	1.755 V	2.091 V
Standard Deviation	0.003 V	0.013 V	0.004 V	0.001 V	0.004 V
Number of Measurements	3	3	3	3	3

The slope of this linear fit is h/e (Planck's constant over elementary charge) and the y-intercept is W₀/e (Work function over elementary charge).

From these 6 data sets of V vs. ν, we obtain these values:

Values	h	W0	σ (h)	σ (W0)
Divided by e	4.102e-15 J*s/C	1.283 J/C	3.2983-16 J*s/C	0.267 J/C
Raw Value	6.571e-34 J*s	0.205e-18 J	5.284e-35 J*s	4.285e-20 J

Compared with the accepted value of 6.626e-34 J*s for h, this value obtained in the experiment is quite close, and is on exactly the right order of magnitude.

These results seem good, aside from the low-intensity anomalies in the first part of the experiment, through which error crept in. If I had more time, I might examine the intensity relationship for other wavelengths. I did take extra measurements in addition to what the experiment demanded, to get more accurate results.

Poisson Distribution Lab

The relevant pages of the lab notebook are 10/1/08, 10/3/08, and 10/6/08.

In this lab, I measured counts of background radiation with a photomultiplier tube. I took multiple readings with multiple dwell times.

Dwell Time	10 ms	20 ms	40 ms	80 ms	100 ms	200 ms	400 ms	800 ms	1 s	2 s	4 s	4 s Revised*	8 s	8 s Revised*
Mean # Counts	0.1729	0.3223	0.6523	1.3262	1.6914	3.2832	6.7139	13.5625	17.0566	35.4111	3.7427e3	82.3503	331.6879	171.8591
σ # Counts	0.4057	0.5694	0.7479	1.0653	1.2175	1.4678	1.8282	2.3434	2.6681	3.5962	9.8137e3	12.3347	1.6070e3	44.8021
Square Root of Mean	0.4158	0.5677	0.8077	1.1516	1.3005	1.8120	2.5911	3.6827	4.1300	5.9507	61.1776	90.7471	1.8212e3	13.1095

• The revised data have all anomalous readings removed. I have included analysis for original data for comparison.

The standard deviation is very close to the mean for small dwell times, but the quantities diverge for very large dwell times.

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