1. Viewing Chamber: Consists of two circular capacitor plates separated by a plastic ring. A flat window in the ring provides a distortion free view of moving spheres; the background is blackened for better visibility. Spheres are injected through a hole in the ring. The metal plates are 4.0 mm apart (this value is precise enough for use in calculations, but can be measured more accurately by disassembling the viewing chamber) and provide a uniform electric field near their center. They are connected to binding posts through a switch and current limiting safety resistors. The chamber is held by two knurled thumb nuts, removable for examination or cleaning.
2. Focusable Microscope: Has a 20X magnification and a reticule with graduations representing 0.5 mm in the viewing field. The microscope housing attaches to the chamber using four nylon screws, and is mounted on a rod which moves in and out for focusing.
3. Light Source: Consists of a 6.3 V incandescent lamp and lens. The hinged cover opens for adjusting and replacing the bulb. The housing is fixed; the socket may be rotated about horizontal and vertical axes for positioning. The coiled vertical filament illuminates the entire area between the top and bottom plates.
4. Sphere Injector: Includes a reservoir for the sphere suspension fluid and a rubber bulb, tubing, and nozzle for spraying the spheres into the chamber. The spheres become charged as they are injected. 5. Switch and Binding Posts: Red (+) and black (-) binding posts provide high voltage connections to the plate. A switch reverses the polarity of the platesÇwhen in the up position, the upper plate is positive; in the down position, it is negative. The center position disconnects the supply and shorts the plates to remove the electrical field between them. CurrentÇlimiting resistors between each binding post and the plates help minimize chance of shock from a properly grounded case. A black binding post on the side of the base is also provided for grounding the case. A pair of blue binding posts provides connections for the lamp.
Figure 1: Circuit Diagram Required Apparatus:
A power supply which provides both a 6.3 V AC/DC outlet for the lamp and a continuously variable high voltage source of up to 200 V DC is required for all experiments stop clock and a voltmeter for measuring the plate voltage will also be needed. A 13 mm (1/2 in.) support rod and tripod base allow the apparatus to be adjusted to proper viewing height.