Attach a piece of gummed paper to one terminal of 

 your coil, and connect the coil to the battery in such a 

 way that the marked end is connected with the copper strip 

 and the opposite end with the zinc strip. 



Determine whether the labeled end is a N or a S pole 

 by testing with the magnetic needle. 



If the marked end of the coil repels the N pole of the 

 magnetic needle, what must be its polarity, N or S ? 



4. Now connect the coil with the battery in such a way 

 that the labeled end is united with the zinc strip. On test- 

 ing with the magnetic needle, do you find that the poles 

 have changed faces ? 



If, at the instant that the coil comes to rest in (2), we 

 could have reversed the direction of the current in the coil, 

 what effect do you think it would have had upon the swing 

 of the coil ? 



In a motor, electricity is applied, and motion results. 

 To-day commercial sewing machines, mills, electric fans, 

 trolley cars, and a host of other well-known inventions 

 owe their efficiency, not to muscular energy, but to elec- 

 trical energy. 



EXPERIMENT 92. THE PRINCIPLE OF THE DYNAMO 

 AND THE TELEPHONE 



The Dynamo. Connect a closely wound coil of wire to 

 a galvanometer as shown in Figure 72. Is there any de- 

 flection of the galvanometer needle ? Thrust a magnet 

 into the coil. Does this cause a deflection ? Withdraw 

 the magnet from the coil. Does this cause a deflection ? 

 Allow the magnet to remain at rest within the coil. Does 

 this cause a deflection ? 



