MAGNETIC EFFECTS OF ELECTRIC CURRENTS 227 



233. How a magnet is produced by an electric current. Has 

 magnetism any relation to electricity? How is an electric 

 current used to make a magnet? Suppose that a current of 

 fifteen or twenty amperes is sent through a copper wire and 

 that the conductor is dipped into a pile of iron filings. It is 

 found that when the wire is raised, the bits of filings cling to 

 the copper. No permanent magnet is present, and although 

 copper is usually considered nonmagnetic, the magnetism the 

 wire possesses must be due to the current in it. When the 

 switch is opened, the filings fall from the wire. The current 

 of electricity causes some disturbance in the region about 

 the conductor through which it is flowing, and this outside 

 effect, which is called magnetism, is a very important part 

 of what is known as an electric current. Therefore, to the 

 heating and chemical effects of electricity already discussed 

 we must add its magnetic effects. 



234. Magnetism in a coil of wire carrying a current. How 

 can the presence of a direct current in a wire be detected ? 

 A horizontal wire through which a current flows is placed 

 parallel to the direction taken by a compass. If the wire 

 with its current is passed about the compass in the manner 

 directed, the N pole of the compass is moved as follows : 



1. If the current flows in the wire from south to north 

 over the compass, the N pole moves to the west. 



2. If the current flows down near the N pole of the 

 compass, the N pole moves to the west. 



3. If the current flows from north to south under the 

 compass, the N pole moves to the west. 



4. If the current flows up near the S pole of the compass, 

 the N pole moves to the west. 



If a loop of wire pointing in the direction taken by the 

 compass is placed around the compass, the needle will move 

 when the switch is closed. Two or more loops will increase 

 the deflection, until the needle reaches a maximum deflection 

 of 90 degrees from the north-south direction. If the current 



