270 



GENERAL SCIENCE 



This induced current going into the receiver causes the 

 diaphragm in it to vibrate the same as did the diaphragm 

 in the transmitter. 



The receiver, as shown in the illustration has a perma- 



nent long U-shaped mag- 

 net with electromagnetic 

 coils on each end of the 

 magnet. The coils are 

 made of a large number 

 of turns of fine wire and 

 each has a soft iron core, 



^ end of whkh j s y 



N 



TELEPHONE RECEIVER 



E, the vibrating diaphragm and BB the 

 electromagnets. 



near the diaphragm. 

 When the current goes around these coils in one direction 

 the permanent magnet is strengthened and the diaphragm 

 is drawn back to the magnet. When the induced current 

 is reversed and goes through the coils in the reverse 

 direction the magnetism of the permanent magnet is 

 overcome and the diaphragm moves out from the poles 

 of the magnet. These changes in 

 the strength of the magnet are 

 made as fast as the diaphragm of 

 the transmitter vibrates, and so 

 the diaphragm of the receiver vi- 

 brates exactly the same as that of 

 the transmitter; thus the same kind 

 of sound waves is transmitted to 

 the air as were made by the voice 

 of the speaker. The extension of the mouthpiece is 

 simply to reflect the sound waves to the diaphragm. 

 The object in the mouthpiece full of holes is to protect 

 the diaphragm. 



TELEPHONE TRANSMITTER 



