ELECTRICAL APPLIANCES AND MACHINES 261 



HELIX OF MANY TURNS OF 

 WIRE 



of the wire around the iron rod, its magnetic force will 

 be doubled. By doubling the current the magnetic force 

 will also be doubled. The 

 strength of an electromagnet is 

 determined by the current or the 

 number of amperes and the num- 

 ber of turns in the coil. 



Electromagnets are usually 

 made in horseshoe form, with a soft iron core extending 

 through each coil. The iron cores are connected by an 

 iron bar called an armature. The cores 

 and armature make a metallic circuit 

 for the lines of magnetic force and 

 prevent them from passing through the 

 air, thus preserving the entire force of 

 the magnet. The iron object lifted 

 serves as a second armature. The coils 

 are wound in such a way that the 

 current passes around them in opposite 

 directions, and therefore the poles of each coil are re- 

 versed. A soft iron core is used because the soft iron 

 is a magnet while a current is pass- 

 ing through the coil, and it loses its 

 magnetism as soon as the current 

 is broken. 



Electromagnets are used for load- 

 ing and unloading iron. A large 

 magnet is fastened to a hoisting SHOWING POLES, LINES 



crane and lowered to a pile of iron. OF FORCE ' * ND DIRC - 



TION OF CURRENT 

 The current is turned through the 



coils of the magnet and the iron adheres to it. The 

 crane lifts the magnet with the iron adhering to it and 

 swings it to the desired place; the current is then cut off 



HORSESHOE 

 ELECTROMAGNET 



