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Reminders from 10-11 Training

Page history last edited by Kim Moore 10 years, 5 months ago

Hello!

Before you run la/b & recitation this week, we wanted to give you a few reminders.

 

1) Recitation: http://www.physics.umd.edu/courses/Phys131/fall2013/Labs/Electric%20forces%20exam%20problem.pdf

(Don't forget to instruct them about which side of the page to begin on.  Add the scaling distance to the front side.  Add part D to the back side.)

 

(break)

 

2) Lab 3, Part 1: Random Motion and Diffusion

Link to documents: http://umdberg.pbworks.com/w/page/68933700/NEXUS%20Physics%20Labs%2C%202013-2014

 

Background readings that might help:

http://umdberg.pbworks.com/w/page/68521483/Coherent%20vs%20random%20motion%20(2013)

(and the links at the bottom of the reading, too!)

 

Notes:

a) EQUIPMENT:

The lab equipment is all nicely prepared, including the solutions for all videos.  Attached is a photo of the staging area (by the refrigerator in the back of the room).  All of the vials are individually labeled, including the bead size, the bead material (S = Silicon, P = Polystyrene), and the solution type (W = Water, Low Glycerol = 15%, and High Glycerol = 30%) (e.g., 2 um SW means 2 micron silicon beads in water).  The bins are also labeled with color-coded sticky notes and video number.  Yellow notes are for the first row of the data matrix (groups 1 and 2), purple notes for the second row (groups 3 and 4), and blue notes for the third row (groups 5 and 6).  The petri dish with a pink label contains the yeast solution vials.

 

All vials have been checked and contain viable solutions.  Remind students to shake the vials before extracting the solution with the micropipettes.  Students should use only a very small amount of each solution, so these vials should be more than sufficient for the full week of labs, all sections included.  Please put the vials back where they belong and refrigerate them between lab sections.

 

Plastic tips and slides are located next to the refrigerator.  Each group will need 4 tips (one for the yeast and one each for the other three solutions).  These should be disposed of at the end of the lab and replaced for the next lab group.  Each group should only need one glass slide--as long as the samples placed on the slide do not touch, the same slide can be used for the yeast and all three videos.  Used slides should be placed in the red container beside the refrigerator.  (Do NOT slide the cover of this container closed all the way, as it will lock tight.)  Some videos may need to be taken twice or other solutions prepared, so a single lab group might occasionally need a second glass slide--but they should need no more than two. (I checked all of the solutions that John prepared--all nine--on a single glass slide without having the solutions overlap.  They can get quite a lot of mileage out of a single slide.)

 

Don't forget to check that all microscopes have been turned off after the videos are collected/before you leave lab.  The bulbs on these scopes are quite expensive and we are trying to prolong their life/use.

 

b) Sample Lab Reports

Some TAs expressed a desire to see some sample lab reports from last year for this lab.  I have attached a bunch.  Week 1 is essentially Lab 3 from last year, and weeks 2 and 3 are essentially Lab 4 from last year.  This may help you get a feel for what the students can accomplish.

 

c) Tricks for getting good videos

0. Do NOT use cover slips for any of these solutions, including the yeast.

1. The students should all be using the 40x optic, and the 1024 resolution is best.  Calibration slides for finding the distance-to-pixel ratio are in the 'my documents' folder, in a 'calibration' folder.  For these calibration slides, the '0' and the '1' are separated by 100 microns.  (For the 40x, 1024 Res calibration slide, students should find that these 100 microns are roughly 700 pixels.)  You will also find images of yeast, 1 um beads, and 2 um beads, as captured by the microscope.  Students can use these as comparison to see that they have focused their microscope properly.

2.  Due to the depth of the liquid sample (drop of fluid), the microscopes can actually focus across a wide range.  Students want to focus as close to the glass slide as possible.  Focusing close to the upper surface of the 'drop' can result in a shaky/vibrating image.  Students may also get a vibrating image if anybody in the group is touching/bumping the desk under the microscope.

3.If the samples on the slide are left over the hot bulb of the microscope for too long, convection currents can create directed motion in the fluid, moving the beads in a non-random fashion.  So videos should be taken fairly soon after the slide is placed on the microscope.

4.  On the down side, ANY beads in a glycerol solution (low or high) will take some time to settle out against the glass slide, where there will be a high enough population to analyze.  So, after the glycerol solutions are deposited on the slide, the students should wait a minute or so to gather the video (and the slide should not be over the heated bulb for this waiting time).

5. Only video 1 will be analyzed in Part 1--so videos 2 and 3 should be SAVED to a flashdrive/email account/dropbox, etc..  Students have been reminded to bring their flashdrives.

 

d) Tricks for speeding up data analysis

1. After the video has been capture by VirtualDub, students can copy the file to the other desktop computer.  Now, analyzing this video file on TWO computers, students can track beads I different halves of the video (one computer does the agreed upon frames for beads on the LEFT side of the video and the other  computer does the agreed upon frames for beads on the RIGHT side of the video).  This cuts the data collection/'harvesting' time in half for the 30-50 beads needed to create good histograms.  Students should not track 'stuck' or 'clumped' beads.

2.  After the data has been 'harvested' using ImageJ, students should combine their data into a single Excel file.  They should make a BACK-UP COPY of their data before beginning to manipulate with Excel.  They should also PLAN AHEAD before trying to do the analysis.  Planning ahead will save them a lot of frustration and wasted effort.

3.Once the data file is at the delta x, delta y, and r stage for all beads, the file can again be split onto two computers so that the histograms can be produced more rapidly.

 

e) Lab jobs

Students should have new jobs for this three week lab.

 

3)  Other Logistics Stuff

a) Does anyone want to be in charge of snacks for this Friday's training?  Email me if you'd like to volunteer.

b) Don't forget to clean the lab up and leave it in neat shape for the next lab group.  You can make your students do most of the work--just give clear instructions!

c) Collect the recitation documents during the break between recitation and lab.

d) Make sure the lab documents don't get all mixed together.

 

That should do it for this week!

~KIM

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