3B Scientific Wimshurst Machine - Manual (Page 2)

4
steady increase of the electrical charge on the tin-foil
segments.
With further rotation all positively charged segments B
arrive at comb S1 and all negatively charged segments A
at comb S2 where all electric charge will be yielded to the
electrode rods with their conductor spheres K1 and K2.
The same processes happen in the lower part of the illus-
tration with the difference that the tin-foil segments A
which pass brush P1’ are now charged positively and the
segments B passing P2’ negatively. The yielded voltage is
dependent on the diameter of the discs.
As a matter of fact the processes described here as a
sequence happen simultaneously.
On the tin-foil segments on disc 1 negative resp. positive
charges are induced below the brushes under the influ-
ence of the charges on disc 2. Those in turn induce elec-
tric charges on disc 2 when they pass the corresponding
brushes. The combs will remove all charges and yield
them to the electrode rods for arc-over between the con-
ductor spheres or to the Leyden jars. The arc-over is de-
pendent on the diameter of the discs.
3B Scientific GmbH • Rudorffweg 8 • 21031 Hamburg • Germany • www.3bscientific.com • Technical amendments are possible
4. Operation
• The Wimshurst machine is supplied ready for use;
only the hand crank has to be attached.
• The position of the diagonal rods must be from up-
per left to lower right at an angle of 45° to the insulat-
ing bar when the hand crank is turned clockwise.
• The isolating switch has to be closed.
• The discharged energy will increase if the Leyden jars
are connected while the length of the arc-over re-
mains the same.
• To determine the polarity of the Wimshurst machine
an electroscope is charged at one of the electrode
rods. If it discharges when touched by a rubbed plas-
tic rod, the polarity was positive, if the charge is in-
creased the polarity is negative, since a plastic rod
rubbed with wool acquires a negative charge. During
operation the polarity never changes. This can hap-
pen only if the Wimshurst machine has not been
used for a considerable period of time.
• Alternatively the polarity can be determined with a
neon glow lamp. It will always glow at the negative
electrode.
5. Notes
• The Wimshurst machine does not work in both direc-
tions of rotation with the same position of the elec-
trode rods. When turning the hand crank clockwise,
the position of the diagonal rods has to be from up-
per left to lower regardless of the side from which
you look at the machine.
• By changing the position of the diagonal rods the
voltage and the current can be adjusted. To yield a
high voltage and a long spark length the angle of the
rods has to be very steep. With more flattened posi-
tioning the current increases.
• When demonstrating the arc-over the negative dis-
charge electrode should be bigger than the positive.
Therefore the electrode rods end in a double sphere.
Position the spheres in such a way that the discharge
occurs from the smaller to the bigger sphere.
• In case of worn brushes cut off a short piece so that
they have a clean metal surface. The brushes should
have contact with the discs while the combs should
be close to them without touching the tin-foil seg-
ments.
• The Leyden jars can be damaged. Then only a small
arc-over can be achieved. In this case check the ca-
pacitance of each jar separately.
• To discharge the Leyden jars completely either con-
nect the two electrode rods for several seconds or
the conductive outer coats of the jars with the up-
per bar.
• In case of failure due to faulty insulation remove any
dust from the Wimshurst machine and blow hot air
against it for several minutes.
• During operation a characteristic smell will be evi-
dent caused by a chemical transformation of the oxy-
gen of the air into ozone.