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Plasma sphere
Glass sphere Ø 20 cm, containing a rarefacted gas mixture. The central electrode has an alternating voltage of 10.000 volt; for this reason it creates electric discharges which spread toward the outside. If you move your finger close to the surface, the discharges concentrate in proximity to your finger because of the conductivity of the human body. So the sphere can be used to distiguish conducting objects from insulating objects. It can be used to prove the existence and the nature of electromagnetic waves, too. In fact, a neon tube moving close to the sphere lights up because of the energy carried by the electromagnetic waves. If you interpose a paper sheet, the phenomenon goes on ,because the waves pass through it. But if you interpose a sheet of conducting metal, such as aluminium, the waves are screened and the phenomenon stops.
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