This demonstration electrostatics set is intended for demonstration experiments in electrostatics in the physics classroom of a general secondary education institution. With the set the teacher shows the class the basic phenomena: the electrification of bodies, the interaction of electric charges, the division of substances into conductors and dielectrics, the uneven distribution of charge over the surface of conducting bodies, the accelerated loss of charge by pointed areas and the appearance of a field around charged objects. The experiment is carried out by the teacher or the laboratory assistant in front of the class; students take part only in separate operations on assignment and under the direct supervision of the teacher. The recommended age of learners is from 10 years, that is pupils of grade 5 and above.
The set consists of eight instruments on insulating bases and a storage box. All the instruments carry only electrodes and indicators and have no built-in power source, and the set needs no mains supply: it has no charge source of its own, so an external electrophorus machine, a Wimshurst generator, is required for work. The bases of the instruments are made of plastic and metal, the electrodes of metal, the insulating posts of plastic, and the connecting elements of copper, rubber and metal. The condition for successful experiments is dry air in the room and clean dry insulating surfaces. 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; storage is at a temperature from +5 to +40 °C and relative humidity that does not exceed 80 %. The set is supplied in a storage box. The service life is 5 years and the warranty period is 12 months from the date of sale.
The set includes a conductor sphere on an insulating holder — 1 pc; a spherical electrode on a post with a base — 1 pc; a needle, that is point, electrode on a post with a base — 1 pc; an indicator sultan, a bunch of paper strips on a rod — 1 pc; a neon lamp on a rubber stopper — 1 pc; electric bells with a movable clapper ball — 1 pc; a set of connecting cables with clamps — 1 set; metal chains for earthing — 2 pcs; the passport with the warranty coupon — 1 pc; and individual transport packaging, a box — 1 pc. The electrophorus machine is not part of the set: a Labotrix electrostatic machine, a Wimshurst generator, or an equivalent one is ordered separately. A candle, matches, rods for electrification by friction and the equipment for the experiments are taken from the standard stock of the physics classroom.
Before a lesson the instruments are wiped with a dry soft cloth, since dust and moisture on the insulators are the commonest cause of failed experiments, and they are placed on the demonstration table within sight of the whole class and several tens of centimetres away from walls, metal furniture, water pipes and radiators. A metal chain connected to the earthing bar of the classroom is prepared as the working tool for discharging and earthing, the electrophorus machine is prepared according to its own instructions, and a trial experiment with the sultan shows whether the installation works. During the experiment the handle of the machine is turned slowly and evenly and the turning is stopped as soon as the desired effect is reached, whether the strips diverge, the lamp flashes or the bells ring, because charge accumulated beyond what is needed only wears the machine out faster.
The set works with the very high voltage created by the electrophorus machine, and a spark discharge is painful, though not lethal, and can cause fright, an involuntary movement or a fall. The installation is never treated as safe merely because the machine has stopped: the discharge spheres of the machine are first brought together, then every electrode, the bells, the sultan and all metal parts are touched in turn with the chain, and the instruments are left connected to the earthing bar for several minutes before the cables are reconnected and before the set is put back into the box. The instruments are held only by the insulating posts and bases, and two instruments or clamps connected to different poles are never touched at the same time. Students with an implanted pacemaker, defibrillator, cochlear implant, hearing aid or another electronic medical device do not take part in the experiments, do not touch the instruments and do not stand near the demonstration table, and this is clarified in advance through the class teacher or the medical worker of the institution; such students watch the demonstration from a safe distance or on a video recording. Smartphones, tablets, laptops and other electronic devices are kept as far as possible from the installation. Experiments are not carried out on a wet floor, with wet hands or in a room with air humidity above 80 %, and the charged installation is not left unattended. The instruments are cleaned with a dry soft cloth after discharging and earthing, without abrasive powders, solvents or acetone; the point of the needle electrode is protected from blunting and bending and the neon lamp from knocks.
