Twentieth century hand-book for steam engineers and electricians, with questions and answers .. . FIGURE 15. we have inserted the magnet and it has come torest the galvanometer needle will return to its normalposition. When we withdraw the magnet the deflec-tion of the needle will be in the opposite direc-tion. If the magnet is inserted or withdrawn witha veiy quick motion, the deflection will be consider-able. If the magnet is very slowly inserted or with-drawn the deflection will hardly be noticeable. The40 ELECTRICITY FOR ENGINEERS 41 same phenomena will occur if instead of moving themagnet
Twentieth century hand-book for steam engineers and electricians, with questions and answers .. . FIGURE 15. we have inserted the magnet and it has come torest the galvanometer needle will return to its normalposition. When we withdraw the magnet the deflec-tion of the needle will be in the opposite direc-tion. If the magnet is inserted or withdrawn witha veiy quick motion, the deflection will be consider-able. If the magnet is very slowly inserted or with-drawn the deflection will hardly be noticeable. The40 ELECTRICITY FOR ENGINEERS 41 same phenomena will occur if instead of moving themagnet, we hold it stationary and move the coil, or ifboth of them be moved towards or from each deflection of the compass needle indicates that acurrent of electricity is passing along the wire, and theexperiments above described show exactly how cur-rents of electricity are produced in dynamos. An electromotive force is induced by rapidly cutting lines of force, that is, by moving either a magnet over a wire or a wire over or near a magnet. The. current in turn is the result of this electromotive forceacting in a closed circuit. A bar of iron becomes anelectromagnet if we wind about it a few turns of wireand cause a current of electricity to flow along thewire, Fig. 16. The magnetism is conceived to consistof lines of force, which leave the bar at one end andenter it at the other, the direction of these linesdepending upon the direction in which the currentcirculates about the bar of iron. The number of theselines of force depends upon the number of ampereturns in the iron bar and on the diameter, length andquality of the iron bar. 42 ELECTRICITY FOR ENGINEERS Ampere turns is a term used to indicate the mag-netizing force; it is the number of turns of wire on amagnet multiplied by the current in amperes flowingthrough these turns of wire. Haskins, in Electricity Made Simple, explains thisthus: If, for instance, we have a current of oneampere flowing through a single turn
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