LAB 1: BROWNIAN MOTION
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
by measurements of a particle’s mean squared displacement.
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.
part III, you analyze the position data, with the help of Logger Pro software for manipulating and
graphing the data.
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!).
tension should hold the cover glass to the slide.
Record the particle size and the ambient
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.
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.
Setting and set the following parameters:
File Name =
+ Serial Number +
capture one image
Maximum Capture images:
Using current date and time as file names
Capture Source Select:
This sets the camera to take 120 photos, 2 seconds apart, when you use Auto Capture.
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