MAGNETISM AND ELECTRICITY 



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end that points north when the magnet is free to turn 

 is called the north pole and the other end the south pole. 



Experiment 51. Suspend a bar magnet in such a way that it 

 is free to move (Figure 153) and determine its north pole and south 

 pole. In the same way determine the poles of another similar 

 magnet. Now bring the North (N) Pole of the first magnet near 

 the N pole of the second and note the 

 result. Test the attraction of the two 

 South (S) Poles for each other. Now 

 test the attraction of the N and S Poles 

 for each other. In the absence of bar 

 magnets, knitting needles may be mag- A N 

 netized and used in the above experi- ^ 

 ment. 



From this experiment the law 

 of magnetic poles may be formu- 

 lated : Like poles repel each other 

 and unlike poles attract. 



Induced Magnetism. A piece 

 of iron becomes a magnet by in- 

 duction when it touches or is 

 brought near the pole of a magnet. Suspend a nail from 

 the end of a strong bar magnet. Another nail may be 

 suspended from the first, a third from the second, and 

 so on. Now hold the first nail firmly and remove the 

 bar magnet by sliding so that the nails will not be jarred. 

 The instant that the bar magnet leaves the first nail 

 the others will drop apart, showing that the nails were 

 strong magnets only so long as they were in contact with 

 the bar magnet. 



Experiment 52. Magnetic Fields. Lay a bar magnet on 

 the table and cover it with a paper, over the surface of which fine 

 iron filings are strewn. When the paper is gently tapped, the filings 

 will arrange themselves in lines reaching from one pole to the 



FIG. 153. Like poles of 

 magnets repel each other; 

 unlike poles attract each 

 other. 



