Biophysics Lab1 - Physics 310 Spring, 2009 LAB 1: BROWNIAN...

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Physics 310 Spring, 2009 LAB 1: BROWNIAN MOTION Goals: To become acquainted with the appearance of Brownian motion via direct observation and measurement of the positions of micron-sized spherical particles in water. To become acquainted with the statistical distribution of particle displacements. To calculate k B by measurements of a particle’s mean squared displacement. Overview: The experiment has three parts. In part I, you photograph, at regular intervals, a single particle, using a microscope with a digital camera driven by computer software. In part II, you use a second software package, Image J, to record the position of the particle in each photograph. In part III, you analyze the position data, with the help of Logger Pro software for manipulating and graphing the data. Part I: Data collection Sample Preparation : Place a sheet of lens paper on the table, and place a dimpled microscope slide, dimple side up, on top. Using a small syringe, transfer a drop or so of the latex sphere solution to the center of the dimple. The drop’s diameter should be no more than ½ centimeter. Cover the sample with a cover slide, so that the drop is squashed between the dimple and the cover slide, without touching the flat area of the microscope slide (if it does, start over!). Surface tension should hold the cover glass to the slide. Record the particle size and the ambient temperature. Camera Preparation : Turn the microscope on, and select the 10X objective. Make sure the condenser mask ring is set to “A” (i.e. brightfield microscopy). Place the Motic calibration slide on the microscope stage, and looking through the eyepiece, focus the microscope on the cross- shaped scale at the center of the calibration slide. Adjust the illumination. Slide the microscope’s eyepiece/camera switch to the camera position. Unplug, and then replug, the USB connection from the camera into the computer. Start up the Motic Images Plus 2.0 software. Go to File Setting and set the following parameters: File Name = Capture + Serial Number + .tiff Every 2 Seconds capture one image Maximum Capture images: 120 Image Size: Auto Checkbox checked : Using current date and time as file names Capture Source Select: MC1001/MC2002 Click OK. This sets the camera to take 120 photos, 2 seconds apart, when you use Auto Capture. Go to File Capture Window . The right window displays a real-time image of your sample. If it appears all white or all black, click the Auto Exposure button on the settings side of the
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capture window. You should see a slightly-out of focus cross. Adjust the microscope focus until the image is sharp. Set Preview to 800 x 600 Capture Size to 1600 x 1200 . Calibration preparation
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Biophysics Lab1 - Physics 310 Spring, 2009 LAB 1: BROWNIAN...

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