Electric Lighting and Power Distribution: An Elementary Manual on Electrical Engineering, Suitable for Students Preparing for the Preliminary and Ordinary Grade Examinations of the City and Guilds of London Institute, Том 1

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Сторінка 3 - MASS AND WEIGHT.— The mass of a body is the quantity of matter in it ; the weight of a body is due to the force of gravity acting upon this matter.
Сторінка 14 - DIFFERENCE BETWEEN ENERGY, FORCE, WORK AND POWER.— It is important that the student should thoroughly understand the meaning of the above terms. Energy is the capacity to do work. Force is one of the factors of work and has to be exerted through a distance to do work, the work being reckoned as the product of the force and the distance through which it has been applied. Work is done when energy is expended or when force overcomes a resistance. Power is the rate of working.
Сторінка 319 - ... sides of the iron cylinder, and the armature back to the iron core, from which they started. 38. Differentially Wound Magnet. — The winding and construction of the extra magnet is the distinctive feature of this repeater. There are two coils of the same number of turns and resistance on the magnet. The end of one coil and the beginning of the next are joined together and connected to a binding post on the base of the instrument. In Fig. 14 is shown an iron core over which two coils are wound...
Сторінка 149 - The current flowing in the coils of wire on the magnet produces what is called a " magnetomotive force," which is proportional to the current and to the number of turns of wire ; and a certain fraction of this quantity is used to send the magnetism through the iron rod and the remainder to send it through the air, or, in other words, every little piece of the magnetic circuit requires a certain magnetomotive force to drive the magnetism through it, and the sum of all these...
Сторінка 64 - FiG 133 that the sense of the field is reversed with reversal of the current, while the direction of the field remains the same. These experimental results may be expressed by the following rule : Grasp the wire with the right hand, the outstretched thumb pointing in the direction of the current; then the fingers indicate the sense of the lines of magnetic induction / \ / \ (Fig. 133). / \ / \ This relation may ® ' °© also be expressed \ / \ / by conceiving the \ / \ / current to be flow- ., ,....
Сторінка 189 - to the passage of an unvarying electrical current, when the coil of insulated wire forming part of the aforesaid instrument and connected to the aforesaid terminals is in all parts at a temperature of 15°'4 C.
Сторінка 190 - Verified, 1894 and 1909,' when on reversing the current in the fixed coils the change in the forces acting upon the suspended coil in its sighted position is exactly balanced by the force exerted by gravity in Westminster upon the iridioplatinum weight marked A and forming part of the said instrument.
Сторінка 226 - Reaistance.) fixed at right angles. A controlling magnet fitted on the left-hand side of the box (Fig. 107), serves to increase or diminish the sensitiveness of the galvanometer. When the magnet's N. pole is uppermost, the galv. will be most sensitive ; if the S. pole is at the top, the deflection of the needle due to any given current will be diminished to nearly one-half. Fig. 109 is a repetition of Fig. 108, except that all those portions of the apparatus not used for the first test (conductor...
Сторінка 23 - CONDUCTIVITY AND RESISTIVITY. The resistivity or specific resistance of a substance is the resistance between opposite faces of a centimetre cube (unit volume) of the substance, expressed in microhms The conductivity or specific conductance of a substance is the reciprocal or opposite of its resistivity, and therefore may be expressed in megamhos, for 1 microhm = 1 mega mho (§ 22).

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