226 



MAGNETS AND CURRENTS 



FIG. 95. A magnet. 



bare in the center (Fig. 95). The points of attraction at 

 the two ends are called the poles of the magnet. 



If a delicately made 

 magnet is suspended as 

 in Figure 96, and is al 

 lowed to swing freely, it 

 always assumes a definite 

 north-and-south position. 

 The pole which point 

 north when the needl 

 is suspended is called th 

 north pole and is marke 



N, while the pole which points south when the needle is su 

 pended is called the south pole and is marked S. 



A freely suspended magnet points nearly north and south. 

 A magnet has two main points of attraction called 

 respectively the north and the south pole. 



The extent of magnetic attraction. If a thin 

 sheet of paper or cardboard is laid over a strong, 

 bar-shaped magnet and iron filings are then gently 

 strewn on the paper, the filings clearly indicate the FIG. 96. The 

 position of the magnet beneath, and if the card- needle. 6 

 board is gently tapped, the filings arrange them- 

 selves as shown in Figure 97. If the paper is held some dis- 

 tance above the magnet, the influence on the filings is less 

 definite, and finally, if the paper is held far away, the filings 

 do not respond at all, but lie on the cardboard as dropped. 



The magnetic power of a magnet, while not confined to 

 the magnet itself, does not extend indefinitely into the sur- 

 rounding region; the influence is strong near the magnet, 

 but at a distance becomes so weak as to be inappreciable. 

 The region around a magnet through which its magnetic 

 force is felt is called the field of force, or simply the magnetic 



