Magnetism and Electricity. with Suppl. Chapter by C.V. Boys

Magnetism and Electricity. with Suppl. Chapter by C.V. Boys

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This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1884 edition. Excerpt: ...250. Wheatstone's Balance or Bridge.--If the points B and D are joined by a wire, no current will pass along the wire when the condition of equation (15) is satisfied, and under no other condition. If therefore B and D are connected with the two terminals of a galvanometer G, fig. 193, and A and C with the platinum and zinc plates of a cell or battery, the needle of G remains at rest under the above conditions. If, say, r3 is diminished, some of the current will pass from D to B, and the needle will turn. This will be prevented by so increasing r2 or diminishing r4, or by doing both, that the above ratio is preserved. This gives us an immediate and incalculably useful means of comparing resistances, and so of measuring resistances by comparison with a standard. In the resistance bridge, or Wheatstone bridge, the simplest method of use is shown in fig. 194. The Fig. 194. figs. 193 and 194 are lettered homologously. Upon a varnished wooden board M is stretched a wire r2 r4, of uniform thickness and free from flaws. This is usually made of German silver, because the resistance of this metal is but little affected by heat. Sliding upon this is an ebonite block e, provided with a pin, which is connected with one pole of the battery, and which is kept up by a spring from touching the wire, but which may be pressed down so as to make contact. The wire r2 r4 is, say, one metre long; C carries a pointer which slides along a scale S divided into millimetres. By reading this scale the relative lengths of r2 and ri are determined. The ends of the wire r2 r4 are soldered to two pieces of brass B and D, which are so massive as to offer no sensible resistance. A is a similar piece. The galvanometer G is connected with B and D, and A is connected with...show more

Product details

  • Paperback | 120 pages
  • 189 x 246 x 6mm | 227g
  • Rarebooksclub.com
  • United States
  • English
  • black & white illustrations
  • 1236884779
  • 9781236884770