348 HOW ELECTRICITY IS USED IN THE HOME 



Experiment. To magnetize an iron bar in the field of another magnet and 

 in the earth's magnetic field. 



Materials: A three-inch length of soft iron. A strong bar magnet. 

 A three-foot length of iron gas pipe or soft iron rod. Compass. Dip- 

 ping needle. Fine iron filings. Hammer. 



Method: (A) Test the three-inch iron rod by dipping it in iron filings. 

 If it shows no magnetic effect, place one end of it very near to one 

 pole of the bar magnet. Tap it two or three times with the hammer. 

 Now test it in the iron filings to see if it has become a magnet. 

 (B) Test the iron gas pipe by holding first one end and then the other 

 near the north end of the compass needle. If both ends attract the north 

 pole of the needle it is not magnetized and is ready to use. If one end 

 attracts while the other repels, its magnetism must be removed. This 

 may be done by holding the pipe horizontally in an east and west 

 direction and striking it with the hammer. After a few trials you 

 will find that its magnetism has disappeared. The compass indi- 

 cates the north and south direction. Place the dipping needle so 

 it is free to swing in this plane. Hold the gas pipe in a position 

 parallel to the dipping needle and strike one or two blows on the end 

 with the hammer. Test to see if the pipe now is a magnet by hold- 

 ing first one end and then the other near the compass needle. 



Results and Conclusion: What are the results in (^4) and (B)? What is 

 one way of magnetizing substances? Why does the dipping needle 

 take the direction that it does? Why point the gas pipe in that same 

 direction ? Why do tools standing in one place in the house sometimes 

 become magnets? 



Magnetic property of an electric current. If a wire 

 connecting the two poles of a dry cell is brought down 

 over a compass in a north and south line, the needle will 

 move just as it would if we brought another magnet near 

 it. This is evidence that a magnetic field surrounds 

 the wire. If the wire is coiled by winding a close layer 

 on a lead pencil and a current sent through it the wire will 

 act like a magnet with two poles. This is shown by bring- 

 ing first one end of the coil and then the other end near 

 the north end of the compass needle, for one end will at- 

 tract and the other end will repel. The coil of wire behaves 



