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In using the old type giant eye magnet for removing intraocular foreign bodies, a disconcerting electric arc and a crackling noise emanate from the foot switch, accompanied by smoke resulting from the burning of the switch contacts. This requires frequent cleaning of the contacts, and at times replacement of the affected parts may be necessitated. A more important consideration is the annoyance to the operator and the frightening effect on the patient.
The physical principles involved in producing these undesirable manifestations are simple, although measurement and calculation are rather complex mathematically. The coil of the magnet is supplied by a direct current, and this creates a powerful magnetic field in the core. When the current is broken, the sudden collapse of this field generates, by self induction, an extremely high voltage, which instantly flows back along the "lead in" wires and jumps the gap which is produced as the
Drachman M, Friedman B. A METHOD OF ELIMINATING ARCING IN THE FOOT SWITCH OF AN EYE MAGNET. Arch Ophthalmol. 1940;24(6):1255–1256. doi:10.1001/archopht.1940.00870060197013
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