Wimshurst Machine - Operation

Operation

The two contra-rotating insulating discs (usually made of glass) have a number of metal sectors stuck onto them. The machine is provided with 4 small earthed brushes (2 on each side of the machine on conducting shafts at 90 degrees to each other), plus a pair of charge-collection combs. The conducting shafts that hold the brushes on a typical Wimshurst machine would form an 'X' on an x-ray photograph; the charge-collection combs are typically mounted along the horizontal and equally contact the outer edges of both front and back discs. The collection combs on each side are usually connected to respective Leyden jars.

Any small charge on either of the two discs suffices to begin the charging process. Suppose, therefore, that the back disc has a small, net electrostatic charge. For concreteness, assume this charge is positive (red) and that the back disc ( lower chain) rotates counter-clockwise (right to left). As the charged sector (moving red square) rotates to the position of the brush ( down arrow tip) next to front disc ( upper chain near center), it induces a polarization of charge on the conducting shaft ( upper horizontal black line) holding the brush, attracting negative (green) charge to the near side ( upper square becoming green), so that positive (red) charge accumulates on the far side (across the disc, 180 degrees away) ( upper square becoming red). The shaft's polarized charges attach to the nearest sectors on disc B, resulting in negative charge on B closer to the original positive charge on A, and positive charge on the opposite side of B . After an additional 45-degree rotation, the positive (red) charge on A (lower chain) is repelled by a positive (red) charge approaching ( near lower chain middle) a positive (red) charge on B ( upper chain). The first collection comb ( arrow-tipped lines to triangles) encountered allows both positive (red) charges to leave the sectors neutral (squares becoming black), and accumulate in the Leyden jar anode (red triangle) attracted to the Leyden jar cathode (green triangle). The charge completes the cycle across the discs when a spark (yellow zigzag) discharges the Leyden jar (red and green triangles).

As B rotates 90 degrees clockwise (left to right), the charges that have been induced on it line up with the brushes next to disc A . Naturally the charges on B induce the opposite polarization of the A-brushes' shaft (viz., negative next to positive and positive next to negative), and the shaft's polarization is transferred to its disc. Disc B keeps rotating and its charges are accumulated by the nearest charge-collection combs.

Disc A rotates 90 degrees so that its charges line up with the brush of disc B, where an opposite charge-polarization is induced on the B conducting shaft and the nearest sectors of B, similar to the description two paragraphs above.

The process repeats, with each charge polarization on A inducing polarization on B, inducing polarization on A, etc. All of these induced positive and negative charges are collected by combs to charge the Leyden jars, electrical charge-storage devices similar to capacitors. It is the mechanical energy required to separate the opposing charges on the adjacent sectors that provides the energy source for the electrical output.