TOPIC:

ID Code: I6-11
Purpose: Demonstrate Brownian motion.
Description: A smoke cell is mounted on a tube connected to a TV camera. On the end of the tube inside the cell is a microscope lens which casts an image of smoke particles in the cell onto the videcon of the TV camera. The focal plane of the microscope/TV system is illuminated by a laser to avoid creation of convection currents by heating with a more powerful light source. A twisted lab tissue is burned and blown out, and while it is smoking the rubber bulb on top of the smoke cell is used to snort smoke into the cell through a tube in the bottom of the cell. After a few seconds convection ceases and Brownian motion is clearly visible on the TV monitor to large groups. The photographs above show the entire system (left), the laser beam entering the smoke cell which is in turn mounted on the video camera (center), and the output of the video camera sent directly to the video frame grabber used to capture the images (right). Clicking on the image at right will play a 30 second MPEG movie of the particles in motion.
Availability: Available