Tuesday, October 27, 2009
Lab 9 Error Budgets & Chopping
Julian's Lab 9 data
If you want to add additional data you recorded to this spreadsheet, drop Julian a note (or me and I will forward).
Lab 9 was all about error budgeting an experiment. An error budget not only is a guide to understanding the sources of uncertainty in an experiment once you have data in hand, but it is also a powerful tool in experiment design. Once you know the big contributors, you can spend some effort to make them smaller, improving the overall experiment. Where's Waldo the Error Budget in this picture?
In experiment 9, chopping was an important technique in reducing noise introduced by drifts. Here is some chopping in action as Jillian alternately allows a polarized and unpolarized beam to be sensed on the photometer in order to assess the noise introduced by laser polarization and intensity drifts.
If you want to add additional data you recorded to this spreadsheet, drop Julian a note (or me and I will forward).
Lab 9 was all about error budgeting an experiment. An error budget not only is a guide to understanding the sources of uncertainty in an experiment once you have data in hand, but it is also a powerful tool in experiment design. Once you know the big contributors, you can spend some effort to make them smaller, improving the overall experiment. Where's Waldo the Error Budget in this picture?
In experiment 9, chopping was an important technique in reducing noise introduced by drifts. Here is some chopping in action as Jillian alternately allows a polarized and unpolarized beam to be sensed on the photometer in order to assess the noise introduced by laser polarization and intensity drifts.
Monday, October 26, 2009
Sunday, October 25, 2009
Friday, October 23, 2009
Lab 8 Material Available
Lab 8 Plan of the Day
Lab 8 Materials - Quantitative Polarization
Self-Assessment Form
I hugely enjoyed this lab - preparing it, and watching you execute it. The teamwork both teams showed as you all worked beautifully together to get high-quality experimental results. It is clear that you all know and respect each other well enough to easily organize yourselves to complete a complex task. My hat is off to you all.
Julian sent me his team's data spreadsheet for sharing:
Team Julian Lab 8 Spreadsheet
Here is what the data looks like (blue squares) compared to a cos^2 law with a phase shift and amplitude that best "fits by eye" (red line).
The data clearly validates the model, Malus' law to within a few percent. A detailed study of this experimental dataset could be done to determine the degree to which the cos^2 law matches the data, perhaps someone will undertake this quantitative task. Also instructive would be a plot showing the uncorrected-for-drifts readings vs angle and the cos^2 law. Since the input beam intensity varied by 40%, the comparison would be graphic in showing the value of performing a chopping experiment. Instrumental drifts are invariably present at some level in every experiment. An experiment seeking the best possible sensitivity must take these drifts into account.
Above is a snapshot of the 2 polarizers with their mounts "blocked" using 1/4-20 bolts in the table to achieve a relatively repeatable position. This technique facilitates rapidly moving each polarizer out of the beam and back in at will without having to fuss much about obtaining correct placement. Just push it (gently) up against the blocking bolts.
Team John emailed me as well. Here is that team's data:
Team John Lab 8 Spreadsheet
Lab 8 Materials - Quantitative Polarization
Self-Assessment Form
I hugely enjoyed this lab - preparing it, and watching you execute it. The teamwork both teams showed as you all worked beautifully together to get high-quality experimental results. It is clear that you all know and respect each other well enough to easily organize yourselves to complete a complex task. My hat is off to you all.
Julian sent me his team's data spreadsheet for sharing:
Team Julian Lab 8 Spreadsheet
Here is what the data looks like (blue squares) compared to a cos^2 law with a phase shift and amplitude that best "fits by eye" (red line).
The data clearly validates the model, Malus' law to within a few percent. A detailed study of this experimental dataset could be done to determine the degree to which the cos^2 law matches the data, perhaps someone will undertake this quantitative task. Also instructive would be a plot showing the uncorrected-for-drifts readings vs angle and the cos^2 law. Since the input beam intensity varied by 40%, the comparison would be graphic in showing the value of performing a chopping experiment. Instrumental drifts are invariably present at some level in every experiment. An experiment seeking the best possible sensitivity must take these drifts into account.
Above is a snapshot of the 2 polarizers with their mounts "blocked" using 1/4-20 bolts in the table to achieve a relatively repeatable position. This technique facilitates rapidly moving each polarizer out of the beam and back in at will without having to fuss much about obtaining correct placement. Just push it (gently) up against the blocking bolts.
Team John emailed me as well. Here is that team's data:
Team John Lab 8 Spreadsheet
Tuesday, October 20, 2009
Lab 8 Prep Package Available
Lab 8 Prep Package
Lab 8 will be a quantitative experiment to determine the angular dependence of the intensity of polarized light transmitted by a polarizing filter. To generate quantitative measurements we will be using the Photometer:
I will be catching a plane right after class, so we will be closing up at 8:30 PM, a little earlier than usual. On Monday, I'll open the lab up an hour early (5 PM) so you can continue any work that was left undone.
Lab 8 will be a quantitative experiment to determine the angular dependence of the intensity of polarized light transmitted by a polarizing filter. To generate quantitative measurements we will be using the Photometer:
I will be catching a plane right after class, so we will be closing up at 8:30 PM, a little earlier than usual. On Monday, I'll open the lab up an hour early (5 PM) so you can continue any work that was left undone.
Lab 7 Wrap-up
Lab 7 worked even better than I hoped it would, exploring the vector nature of polarization with hand-held plastic polarizing film. One of my goals is to give you enough "touches on the ball" so you can develop a feel for how optical phenomenon behave. You have plenty of experience with balls, wheels, blocks, and so on. But we all have only limited opportunities in everyday life to manipulate light beyond turning on and off a switch. Every now and then just walking around you will see a curious optical phenomenon. I encourage you to "step outside the box" and take a closer look, take the time to come to some conclusions, and thereby add to your experiential base. You may want to carry around a small piece or two of polarizing film in your wallet just to have a fun investigatory tool.
LOL Labz
U r makin' me haz seen the lite!
LOL Labz
U r makin' me haz seen the lite!
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