3.1 Sample Production

A fairly dilute samples of the colloids is required so that their motion is not heavily influenced by other large groups of colloids. A typical concentration of colloids for this experiment is about 0.2% by volume. The colloids are shipped in at 10% concentration.

3.2 Microscope

We have an OMAX digital microscope (shown in Figure 1) with 4x, 10x, 40x, and 100x objectives on a rotating mount. You will probably only use the 10x and 40x for this experiment. The microscope has a camera and USB connection so that the user doesn’t have to look through the eyepieces. There is a switch on the side of the microscope to turn on a light underneath the stage to illuminate your sample. The stage can move in 3-axes using the knobs shown in Figure 1.

Figure 1: The microscope you will be using, with the location of some of the controls.

Images from the camera are shown on the PC. This video stream can be recorded at the frame rate given at the bottom of the screen. The fastest way to record data is to save the capture via video.

3.3 Magnetic Field

At the time of writing this lab manual, I have not found a clever way to jam a coil of wires beside the microscope objective that would provide a large enough field to make the colloids form into chains. As such, please use the bar magnet held beside the sample to generate the magnetic field.