A manually driven Wimshurst electrophorus machine with 235 mm discs and Leyden jars on a common insulating base, for demonstration experiments in electrostatics in the school physics classroom.
This Wimshurst generator, an electrophorus machine, is intended for demonstration experiments in the field of electrostatics. The machine accumulates a considerable electric charge and provides a high-voltage supply for observing the distribution of charge over conductors, the lines of force of an electric field, the flow of electricity from sharp points and arc discharges. It is used in physics lessons in classrooms of the natural science profile and is placed on the demonstration table of the teacher; the machine is operated by a teacher or another adult who has been instructed in occupational safety, students are admitted to work only under constant adult supervision, and the recommended age of learners is from 10 years, that is pupils of grade 5 and above.
Every unit of the machine is fixed on strong posts made of electrical insulating material, and these posts are joined together with the Leyden jars on a single massive base, also made of insulating material. The machine is equipped with discs 235 mm in diameter with a conductive coating that provides reliable operation in conditions of raised humidity; the discs carry conductive sectors that interact with the neutraliser brushes. The design provides for the use of Leyden jars to accumulate charge and of dischargers with insulating handles for safe work with high voltage.
The maximum voltage is 10000 V. The discharge distance is 55 mm at a humidity of 65 % and 30 mm at a humidity above 80 %, and the working temperature range is from -10 to +40 °C. The discs are made of a conductive composite with increased adhesion, the built-in capacitors are Leyden jars whose capacitance can be changed, and the drive is a manual one with a belt transmission. Operating conditions are the premises of an educational institution at an air temperature from +5 to +40 °C and relative humidity from 40 to 60 % without condensate. Marking and operating documentation are in Ukrainian, the marking carries the trade mark, the model and a place for the inventory number, and the documentation comprises the passport with the warranty coupon and the operating instructions. The machine is supplied in an individual corrugated cardboard box with the contents fixed in place, the discs and the body may be wiped with a dry or slightly damp cloth, the service life is 5 years and the warranty period is 12 months from the date of sale.
The set includes the body with the discs and shafts — 1 pc; dischargers with insulating handles — 2 pcs; conductors, that is charge collectors — 2 pcs; Leyden jars — 2 pcs; connecting bars for adjusting the capacitance — 2 pcs; neutraliser brushes — 4 pcs; the passport with the warranty coupon — 1 pc; and individual transport packaging — 1 pc. The machine requires no assembly before use, and repair and replacement of worn parts are carried out by a specialised service centre.
Before work the machine is placed on a horizontal stable surface protected from wind and moisture, dust and assembly residues are removed with a soft dry cloth, since contamination of the discs or brushes reduces the efficiency of electrification, and both dischargers are set in the offset positions so that the front and rear brushes cross at a right angle and the brushes are inclined at 45°. A machine that has been kept in a damp environment or has become frozen is dried and then held at room temperature for one hour before use. The discharge spheres are moved apart to a starting distance of 10 to 15 mm and the handle of the drive is turned slowly and evenly, so that the brushes contact the conductive sectors of the discs and charge accumulates on the conductors until sparks appear between the discharge spheres. Moving the spheres apart slowly shows the spark growing longer, and in a darkened room bright sparks are seen near one sphere, marking the positive charge, and a violet glow near the other, marking the negative charge. Joining the outer conductive linings of the Leyden jars with the bars increases the total capacitance and makes the spark brighter and longer, while moving the bars outwards reduces the capacitance and shortens the spark. To stop, the discharge spheres are moved to the maximum distance, the speed of turning is reduced and the handle is released so that the discs stop by themselves; after the experiment the two discharge spheres are brought into contact to neutralise the residual charges and make the machine safe.
The machine generates a voltage over 10000 V, and although the current is small and not lethal, a discharge is accompanied by a painful reaction of the body, so the hands are kept only on the insulating handles of the dischargers, the metal elements under voltage are not touched, the position of the discharge spheres is changed slowly step by step, and the head, face and uncovered parts of the body are not brought close to the dischargers during the experiment. While the drive handle is turning, long hair, clothing and small objects are kept at a safe distance from the moving discs, no objects are inserted between the discs or into the slots, and the mechanism is never stopped by hand. It is forbidden to turn the machine too fast, which disturbs the contact of the brushes and can damage the discs and the mechanism, to dismantle, readjust or modify the design, to leave the machine under voltage without an adult present, and to use it in explosive environments or near flammable materials. The body, the discs and the sectors are wiped with a soft dry cloth once a month, dust is removed from the brushes with a soft brush or air, stubborn contamination is removed with a cloth moistened with distilled water and then wiped dry, and abrasive powders, solvents, alcohol and chlorine-containing agents are never used. The clean and dry working surface of the machine has to be maintained at all times, because moisture always worsens the electrification of the device.
