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Wimshurst Machine
# 5A50.10

Description: Two circular discs, made of Plexiglass and with a diameter of 31cm, are mounted parallel with one another and with a short distance apart on a horizontal axis. The axis rests on two struts which are attached to the base plate. Each disc is connected independently to the drive shaft via belts and pulleys. One of the belts is crossed and as result the discs rotate in opposite directions when the crank is turned. The external surfaces around the perimeters of both discs are covered with metal foil stripes. In front of each disc a conductor arm is mounted diagonally, which can be rotated on their axes and which are fitted with metal brushes that drag over the metal foil stripes of the discs. The front end of the axle is extended and connected with the insulating bar by means of a knurled screw. The charge is collected from the two discs by metal brushes located at the end of the insulating bar. These brushes are connected to the two ball ended electrode rods and by means of the lever rods to the two Leyden jars. The Leyden jars of glass are coated with metal foil outside and inside. the two terminals are connected to the outer coating of the Leyden jars and are used to draw off an AC voltage. Regularly the terminals are short circuited to enable a DC voltage to be drawn off. The maximal spark length obtainable with this machine is about 120mm. The short circuit current is approximately 30 microamps.

Instructions: The best position for the diagonally mounted conductor arms is reached when they cross at an angle to the insulating bar of approx. 45 degrees (perpindicular to each other). When the Leyden jars are connected more electrical capacity is discharged by arching, but without increasing the length of the spark.

Purchased/Built: purchased

Setup Time: 1 hour

Quant. in Demo Room: 1

Source: Central Scientific

Demo References
The Video Encyclopedia of Physics Demonstrations Disc 17-04 Shows Wimshurst machine. Animation sequence shows principles of operation.
Freier and Anderson Ea-22 An explanation of how the Wimshurst charges by induction.

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