A Treatise on Coal Mining, Partes26-33

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Colliery engineer Company, 1900
 

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Página 27 - As a unit of current, the international ampere, which is onetenth of the unit of current of the cgs system of electromagnetic units, and which is represented sufficiently well for practical use by the unvarying current which, when passed through a solution of nitrate of silver in water, and in accordance with accompanying specifications, deposits silver at the rate of 0.001118 of a gramme per second.
Página 2 - ... a coil, upon the rate of change in the number of lines of force which pass through the coil. The strength of the current which flows is then given by Ohm's law ; that is, it is equal to the induced EMF divided by the resistance of the circuit.
Página 61 - ... the foot-pound. The work done in raising any mass through any height, is found by multiplying the number of pounds in that mass by the number of feet through which it is lifted.
Página 4 - From these experiments are derived the following laws: When two dissimilar substances are placed in contact, one of them always assumes the positive and the other the negative condition, although the amount may sometimes be so small as to render its detection very difficult.
Página 12 - ... the direction of the current in the conductor is reversed, the north pole will point towards the east. Since, in this example, the north pole of the needle tends to point towards the east, the current must be flowing from the north to the south.
Página 19 - In the actual machine, each pair of coils, as it passes through the position of least action (ie, when its plane is at right angles to the direction of the lines of force in the field, and when the number of lines of force passing through it is a maximum, and the rate of change of these lines of force a minimum) is cut out of connection.
Página 1 - FIO. 973. of a pulley, will not generate a current, because there is no change in the number of lines of force passing through the loop. But if, as in Fig. 974, the coil be tilted in its motion across the uniform field, or rotated around on any axis in FIO.
Página 47 - II, inserted here for convenient reference, gives the dimensions, weight, and resistance of pure copper wire. The weights given are, of course, for bare wire. The first column gives the B. & S. gauge number, the second the diameter in mils.
Página 12 - A certain series-wound motor is tested with a Prony brake, the distance from the center of the shaft to the point where the arm of the brake rests on the scale platform being 36 inches. The brake is tightened until the pressure on the platform is 27 Ib.
Página 56 - ... the strength of the field, (2) the number of conductors, (3) their mean distance from the axis of the armature, and (4) the amperes in each conductor. In any given machine, the second and third conditions are constant, so that the torque depends on the strength of the field and the current. If the armature is stationary, the EMF required to send the current through the winding is only that necessary to overcome the drop, which is due to the resistance of the winding. If the torque exerted by...

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