MAGNETISM AND ELECTRICITY 



205 





right hand so that the thumb points in the direction in 

 which the current is flowing, the fingers will encircle the 

 wire in the same direction as do the magnetic lines. 



The Electromagnet. - 

 The magnetic effect of an 

 electric current is of great 

 practical value in its many 

 applications. We have 

 learned that a wire carry- 

 ing a current is sur- 

 rounded by a magnetic 

 field, and we should ex- FlG 178 ._ If the helix is free to turni 



pect that if We have a ^ w ^ arrange itself in a north and south 

 , .... . position. 



number of wires in a given 



space, all carrying currents in the same direction, the 

 magnetic field would be strengthened. The same effect 

 may be obtained by winding a single wire in the form of 

 a helix (Figure 178). The wire should be insulated to 

 avoid the short-circuiting of some of 

 the turns should they come in contact 

 with each other. If this helix is free 

 to turn, it will behave, like a mag- 

 netic needle in taking a north and 

 south position. A bar of soft iron 

 placed in the coil becomes a tempo- 

 rary magnet. Such a magnet is called 



FIG. 179. An Electro- _. 



magnet of the Horseshoe an electromagnet. The greater the 

 number of turns of the wire in the 

 coil the stronger will be the magnetic field and conse- 

 quently the stronger will be the electromagnet. 



Experiment 57. Make an electromagnet by winding a bar of 

 soft iron in the shape of a horseshoe with insulated wire (Figure 

 179) and test its lifting power. 



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