A manual of practical medical electricity - the Röntgen rays and Finsen light (1902) (14803511563)

Identifier: manualofpractica00turn (find matches)

Title: A manual of practical medical electricity : the Röntgen rays and Finsen light

Year: 1902 (1900s)

Authors: Turner, Dawson

Subjects: X-Rays Electrophysiology Electrosurgery Electric Stimulation Therapy Electrotherapeutics X-rays Electrophysiology Electrosurgery

Publisher: New York : William Wood & Company

Contributing Library: Francis A. Countway Library of Medicine

Digitizing Sponsor: Open Knowledge Commons and Harvard Medical School

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external resistance is low, it is the internalresistance to which we must attend. Upon what doesthis depend, and how can it be diminished ?The factors to be considered are : 1. The conducting nature of the fluid or fluids, andpresence or absence of a diaphragm through which thecurrent has to travel inside the cell. (See p. 60.) Thusa bichromate or a Groves cell has very much less internalresistance than a Daniell. 2. Distance of the plates from each other ; the nearerthey are, the less fluid the current has to go through, andthe less the resistance. Current-Strength 69 3. Size of the plates immersed in the fluid ; the greaterthe area the less the resistance. For our present purpose, then, we choose cells whichfrom their nature have a low internal resistance, such asthe bichromate and the Grove, and we make them as largeas we conveniently can to increase the area of their plates,but accumulators are to be preferred. Further, weconnect our cells in what is termed -parallel arrangement,

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Fig. 31.—Three Cells in Parallel. mstead of connecting copper to zinc; we join all thecopper plates together to form one + electrode, and all thezinc plates together to form the — electrode. (See Figs. 31and 32.) By this means we form, as it were, one large cellwith several copper and zinc plates, and as, other thingsbeing equal, the amount of resistance in any cell dependsupon the area of the cross-section of the plates immersed,so we have virtually reduced the resistance by the numberof cells we have in this manner coupled. If one Daniellhas a resistance of five ohms, five Daniells so connected 70 A Manual of Practical Medical Electricity

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1902

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