CHAPTER XVI 



USES OF ELECTROMAGNETS 



We are all familiar with small magnets that attract iron 

 filings and mysteriously support strings of tacks, and we 

 have laughed at magnetic toys that perform strange antics. 

 Few realize, however, the useful part magnetic force plays 

 in our lives when it works hand in hand with electricity. 



Today electricity and magnetism have been put in dou- 

 ble harness. They drive many of our household appli- 

 ances, give us our telephones and telegraphs, run our street 

 cars and drive machinery in many of our factories. 



Electricity and magnetism are not the same although they are 

 closely related. Their relationship was not understood or 

 explained until the early part of the 19th century (1819). 



A Danish physicist, Oersted by name, noticed that a compass 

 needle was more or less affected when brought near a wire 

 through which a current of electricity was flowing. He noticed 

 that when a wire connecting the poles of an electric cell was held 

 over a magnetic needle, the north pole of the needle was deflected 

 toward the west if the current in the wire was flowing from south 

 to north, and towards the east if the current flowed from north to 

 south. This led to the discovery of the magnetic effect of electric 

 currents. Oersted showed clearly, by experiment, that every elec- 

 tric current is surrounded by magnetic force which influences 

 the direction of any magnetic needle near which the current 

 passes. 



Experiment to Show the Effect of an Electric Current on 

 a Magnetic Needle. Sprinkle iron filings on a piece of card- 

 board about a foot square, through the center of which a wire 

 connected with a powerful battery has been passed. A storage 

 battery or several dry cells connected in a battery are needed to 

 show good results. Turn on the current and tap the edge of the 

 cardboard gently. Notice what happens to the iron filings. Place 

 a small compass at different positions on the cardboard and 



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