A Textbook on Mining Engineering, Τόμος 4

International Text Book Company, 1900

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Άλλες εκδόσεις - Προβολή όλων

Συχνά εμφανιζόμενοι όροι και φράσεις

Δημοφιλή αποσπάσματα

Σελίδα 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.
Σελίδα 17 - 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.
Σελίδα 5 - ... field in the direction of the lines of force ; but if the effect is to increase the number of lines of force that pass through the coil, the current will circulate around in the opposite direction. For example, in the diagram, Fig. 3, when the coil is inserted into the magnetic field, thereby increasing the number of lines of force which pass through the coil, the current circulates from b around the coil to a, and thence through the galvanometer to b again; when the coil is withdrawn and the...
Σελίδα 6 - 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...
Σελίδα 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 diff>cult.
Σελίδα 22 - Hydromechanics and Pumping. The advantages of inside and outside packing, of directacting and fly-wheel pumps, and other facts regarding pumping machinery are there thoroughly treated. For the present we have to deal with electric pumps only; but it may not be amiss to state under what conditions the electric system is superior to the other systems. If there is but a limited amount of pumping to be done, it is not advisable to install any very expensive plant, as the interest on the cost might exceed...
Σελίδα 40 - ... 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...
Σελίδα 7 - A A' gets to the position of least action, it is disconnected from the circuit by seg ment a passing out from under brush 3, leaving coil B B' and coil C C' in series. However, as the distance between brush 3 and brush 2 is only slightly greater than the span of one segment, coil A A...
Σελίδα 52 - E, in this case, represents the loss or drop of potential in volts between the two points. If any two of these quantities are known, the third can be readily found, as already shown in connection with Ohm's law.

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