The Galvanometer: A Series of Lectures

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McIlroy & Emmet, 1894 - Electric measurements - 112 pages
 

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Page 98 - As a unit of electromotive force, the international volt, which is the electromotive force that, steadily applied to a conductor whose resistance is one international ohm, will produce a current of one international ampere, and which is represented sufficiently well for practical use by ^-J of the electromotive force between the poles or electrodes of the voltaic cell known as Clark's cell, at a temperature of 15...
Page 109 - One of the strips, for example, A, is exposed to radiation, while the other is screened. One notes the deflection of the galvanometer, which becomes constant in about fifteen seconds. A is then also screened, and by means of the current is brought to the same temperature to which radiation had previously brought it. The strength of the current producing this rise of temperature is then measured. The advantage of this arrangement is that the same strip is warmed by means of radiation and then through...
Page 53 - Ibid. obtained with each respectively ; this being effected by varying the intensity of the magnetic field in a known ratio, and comparing with it the unknown current. • The present instrument consists essentially of two parts — 1st, a coil of thick wire, through which the current to be measured is allowed to pass, it being fixed upright at the end of a wooden platform, with about one-half only of the coil projecting above it ; and, 2nd, of a "magnetometer.
Page 109 - ... Variation of the Method. — One of the strips, for example, A, is exposed to radiation, the other, B, is screened ; the deflection of the galvanometer is observed after the thermocurrent has become constant. The quantity of heat which A has received is calculated from Newton's law of cooling, where 0 is the difference of temperature indicated by the galvanometer, and k is the constant of cooling of the strip. If we now send a current through A, without making any change of conditions, the difference...
Page 108 - ... possible, however, to carry on the investigation without any difficulty, using only one galvanometer, a plan which I pursued in the case of the first apparatus which I constructed. Fig. 2 gives a diagram of the connections, while Figs. 3, 4, 5, and 6 show more in detail the arrangement of the apparatus. The metallic strips, A and B, cut simultaneously from two thin sheets of platinum laid one upon another, are 0.154 cm. wide and 1.80 cm. in length. They are blackened in the usual way upon the...
Page 69 - ... the construction of a sensitive galvanometer are form and size of coil, size of wire, the kind of magnet and the dimensions and construction of the needle system, the astaticizing of the magnet system, the shielding of the system from influences due to the earth's field and neighboring objects, etc. The proper form and method of winding galvanometer coils to secure a maximum effect from a given weight or resistance of copper has been thoroughly discussed by...
Page 74 - ... procedure be carefully followed a highly astatic pair may always be obtained. The two small magnets thus made from each piece were used, one in each of the elements of the astatic system. The galvanometer had a resistance of 15 ohms with its coils in series. When so arranged, and with a half-period of seven seconds, and scale distance of 120 cm., a deflection of i mm. corresponded to 6 x io~10 amperes.
Page 74 - Vol. 1. p. 437. just before being used, — a precaution which should always be taken in preparing for any important work requiring the last degree of sensitiveness, and care was taken to send no currents of any ordinary strength through the instrument. In the preparation of the magnets the following precautions were taken. Piano wire y mm.
Page 56 - VOLTMETER, VOLTAGE OF A BATTERY. This coil turns, when a current passes through it. in the strong field between the poles of a powerful permanent magnet. in the base are two resistance coils, one or the other of which is always in series with the movable coil, depending upon which scale is used — the 150 or 5 volt scale. Caution. — To prevent bending the pointer by violent action, always test first with the 150- volt scale.
Page 107 - B is protected by a screen, we may restore the balance of temperature which has been disturbed by the absorption of heat on the part of A, by sending a current of proper intensity through B. When the temperatures are the same, then the amounts of energy which A and B have received...

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