3B Scientific Wimshurst Machine - Manual

3
3B SCIENTIFIC® PHYSICS
U15310 Wimshurst Machine
®
Instruction Sheet
The Wimshurst machine serves as a source of safe, high
DC potentials for numerous experiments in the area of
electrostatics.
1. Safety instructions
• Caution! Sensitive electronic equipment (computers,
calculators, digital measuring instruments etc) can be
damaged by high-frequency interference peaks,
caused by voltage flashovers.
• Use only naphtha to clean the plastic parts. Never use
solvents for cleaning.
• Store your Wimshurst machine in a dry, dust free place.
Do not expose it to direct heat sources (sunlight, ra-
diator).
2. Description, technical data
The Wimshurst machine is made up of two equally large,
parallel transparent acrylic discs
1 which are fitted on a
horizontal axle and slightly spaced from each other. The
axle rests on two wooden pillars mounted on a base
plate.
The Wimshurst machine is operated by hand crank with
both discs separately connected to the drive shaft by
means of two belts and two belt pulleys. One belt is
twisted, so that the discs rotate in opposite directions
when the hand crank is turned.
Tin-foil segments are placed around the circumference
of the outer surfaces of the discs. In front of each disc a
diagonal rod
6 with two metal brushes is pivoted on
the axle with brushes sliding over the tin-foil segments.
Connected to the axle is a horizontal insulating bar
2 in
front of the Wimshurst machine with a rod holding combs
1 Transparent acrylic discs with tin-foil segments
2 Insulating bar
3 Electrode rods
4 Leyden jars
5 Isolating switch
6 Diagonal rod with metal brushes
7 Rod with combs
8 Switch levers to connect the Leyden jars
and the combs
6
5
1
4
3
2
7
8
7 on either end to draw off the electric charge. The dis-
tance from the discs is adjustable and should be a few
millimeters. They are connected to the electrode bars
3 . The electrode bars end in double spheres, between
which the the arc-over occurs. The Leyden jars 4 (high-
voltage capacitors) can be hooked up to the electrode
bars by means of switch levers
8 . The isolating switch
5 can be thrown to connect the Leyden jars.
Diameter: 310 mm
Spark gap: max. 120 mm
Dimensions: 360 mm x 290 mm x 450 mm
Short circuit current: approx. 30 µA
Weight: 3.4 kg
3. Operating principle
During operation an initial small charge is steadily in-
creased by induction processes until the max. operating
voltage is obtained. The operating voltage is limited by
arc-over, drawing of current and insulation resistance.
In order to make it easier to understand of the function-
ing principle of the Wimshurst machine, we imagine the
discs to be hollow cylinders which rotate around a com-
mon axle in opposite directions (cf. illustration).
When the tin-foil segment B1 has been charged posi-
tively by friction with the brush P2, it will move succes-
sively to positions B2 and B3. In position B3 it will be
opposite segment A1 which is connected to earth via
brush P1 and charged negatively. A1 will retain its nega-
tive charge when it moves to positions A2 and A3.
In position A3 it will charge segment B1 positively by
means of electric induction.
This process repeats itself constantly which leads to a
9/03 ALF