2l8 



MODERN ELECTRICAL INVENTIONS 



FIG. 86. 

 Coil and 

 soft iron 

 rod. 



If a soft iron nail (Fig. 86) or its equivalent is slipped 

 within the coil, the lifting and attractive power of the 

 coil is increased, and comparatively heavy weights 

 can be lifted. 



A coil of wire traversed by an electric current and 

 containing a core of soft iron has the power of attract- 

 ing and moving heavy iron objects; that is, it acts 

 like a magnet. Such an arrangement is called an elec- 

 tromagnet. As soon as the current ceases to flow, the 

 electromagnet loses its magnetic power 

 and becomes merely iron and wire 

 without magnetic attraction. 

 If many cells are used, the strength of the 

 electromagnet is increased, and if the coil is 

 wound closely, as in Figure 87, instead of loosely, 

 as in Figure 85, the magnetic strength is still 

 further increased. The strength of any electro- 

 magnet depends upon the number of coils wound 

 on the iron core and upon the strength of the 

 current which is sent through the coils. 



To increase the strength 

 of the electromagnet still 

 further, the so-called horse- 

 shoe shape is used (Fig. 88). In such an ar- 

 rangement there is practically the strength 

 of two separate electromagnets. 



The electric bell. The ringing of an 

 electric bell is due to the attractive 

 power of an electromagnet. By pushing a 

 button (Fig. 89, B) connection is made with 

 lft G gg _ A horseshoe a battery, and current flows through the 



electromagnet strong w j re woun( J on tne i ron spO ols, and further 

 enough to support heavy 



weights in a pan. to the screw P which presses against the 



FIG. 87. An 

 electromagnet. 



