Everything about The Wimshurst Machine totally explained
The
Wimshurst machine is an
electrostatic device for generating high
voltages developed between 1880 and 1883 by
British inventor James Wimshurst (
1832 –
1903). It has a distinctive appearance with two large contra-rotating discs mounted in a vertical plane, two cross bars with metallic brushes, and a spark gap formed by two metal spheres. It is based on the
triboelectric effect, where charge accumulates when two dissimilar materials rub against one another.
Description
These machines belong to a class of generators called
influence machines, which create
electric charges through
electrostatic induction, or
influence. Earlier machines in this class were developed by
Wilhelm Holtz (1865 and 1867),
August Toepler (1865), and J. Robert Voss (1880). The older machines were less efficient and exhibited an unpredictable tendency to switch their polarity. The Wimshurst didn't have this defect.
In a Wimshurst machine, the two insulated disks and their metal sectors rotate in opposite directions passing the crossed metal neutralizer bars and their brushes. An imbalance of charges is induced, amplified, and collected by two pairs of metal combs with points placed near the surfaces of each disk. These collectors are mounted on insulating supports and connected to the output terminals. The positive feedback increases the accumulating charges exponentially until the dielectric breakdown voltage of the air is reached and a spark jumps across the gap.
The machine is self-starting, meaning that external electrical energy isn't required to create the initial charge. However, it does require mechanical
power to turn the disks against the electric field, and it's this energy that the machine converts into electric power. The output of the Wimshurst machine is essentially a constant
current that's proportional to the area covered by the metal sectors and to the rotation speed. The insulation and the size of the machine determine the maximum output voltage that can be reached. The accumulated spark energy can be increased by adding a pair of
Leyden jars, an early type of
capacitor suitable for high voltages, with the jars’ inner plates independently connected to each of the output terminals and the jars’ outer plates interconnected. A typical Wimshurst machine can produce sparks that are about a third of the disk's diameter in length and several tens of microamperes.
Further Information
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