93 



attracts 



The S pole of the magnet or the N pole of the magnetic needle, 

 repels 



<i '< Q < 



Do poles of like or unlike names attract each other ? 

 Do poles of like or unlike names repel each other ? 



EXPERIMENT 90. OTHER RESPECTS IN WHICH AN ELEC- 

 TRIC CURRENT IS LIKE A MAGNET 



We have seen that a current-carrying wire is able to de- 

 flect a magnetic needle and to attract iron filings. If we 

 can show experimentally that such a wire has lines of force, 

 and in addition that it obeys the laws of magnetic attrac- 

 tion, we shall be justified in saying that a current-bearing 

 wire is in most respects equivalent to a magnet. 



For this purpose, we must have a strong current. The 

 electricity furnished by cells, while strong enough for elec- 

 tric bells and for most laboratory purposes, is relatively 

 weak. Elevators, electric lights, etc., require strong cur- 

 rents, and for this reason electricity is generated on a large 

 scale in other ways. Most large buildings have their own 

 electric plant and produce their own electricity, sending it 

 from the generating room to distant parts of the building 

 by means of insulated wires hidden in floors or walls. 



i. In your laboratory desk are wires which connect with 

 a central source of electricity. Attach the closely wound, 

 insulated coils used in Experiment 86 to the desk source of 

 electricity and see whether the ends of the coil affect the 

 magnetic needle as the bar magnet did. That is, does one 

 end of the coil always attract the N pole of the magnetic 

 needle and repel the S pole ? Does the opposite end of 



