The Electrician Volume 13

The Electrician Volume 13

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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: ...of the arc, which is chiefly composed of highly-heated carbon vapour and volatilised carbon. Motors and secondary batteries have an apparently higher resistance, due to back E.M.F., while, on the other hand, the hot resistance of an incandescent lamp (or resistance when the current necessary to produce the proper candle-power in the lamp is flowing through it) is only about one-half the cold resistance as measured on the bridge. ' Let us now take some measurements on a circuit of arc lamps, say six, working off a Brush dynamo, using Ayrton and Perry's ammeter and voltmeter. In any part of the circuit we insert the ammeter, so that the whole of the current to be measured passes through it, as in Fig. 11. Remove the keeper, and turn the current on. The pointer immediately moves from zero to the right or left, as the case may be, and almost instantly, if the current is steady, comes to rest. In this instrument and also in the voltmeter the needle is deflected towards the terminal, at which the current enters. This of course means in the case of the voltmeter that the terminal, to which the needle points, is at a higher potential than the other. Thus in Fig. ll the current is entering at the right-hand screw of both the ammeter and voltmeter, showing the current to be running in the direction of the arrows. The needle of the ammeter comes to rest in the present case at 7 on the scale. On referring to the table supplied with the instrument we find that 7 to the right means l0'l amperes. If we now want to know the E.M.F. at the binding screws H of any particular lamp we take the voltmeter and join its terminals to the said binding screws. This may be done with quite fine wire (20 to 22 B.W.G.), as only a very small current passes, and the...
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Product details

  • Paperback | 680 pages
  • 189 x 246 x 35mm | 1,193g
  • United States
  • English
  • black & white illustrations
  • 1236858379
  • 9781236858375