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Our Surroundings 



A telephone receiver usually consists of a steel U-shaped mag- 

 net, on each arm of which is a coil of many turns of fine wire. 

 This wire is connected to those extending to the transmitter. 

 Across the ends of the magnet there is supported a thin disc of 

 soft iron called the diaphragm. This diaphragm is quite close to 

 the ends of the magnet, but does not touch them. The magnet 

 and diaphragm are housed in a hard rubber case. 



When the increasing and decreasing current from the trans- 

 mitter flows through the coils of the receiver, the magnet in the 

 receiver becomes stronger and weaker accordingly. The soft 

 iron diaphragm of the receiver is made to vibrate by the varia- 

 tion in the strength of the magnet. The vibration of this 



American Telephone and Telegraph Co. 



VIBRATIONS CAUSED BY SOUND WAVES 



diaphragm sets up sound waves like those which cause the 

 transmitter diaphragm to vibrate. 



The telephone wires do not carry sound, but they carry a 

 varying electric current. At the speaking end of the telephone 

 there is sound in the form of sound waves from the voice. These 

 sound waves cause a vibration of the diaphragm of the trans- 

 mitter, which in turn causes variations in the current passing in 

 the circuit to the listening end. This varying current causes the 

 diaphragm of the receiver to vibrate, and produces sound waves 

 in the air, thus reproducing the words of the speaker. 



The telephone is an excellent illustration of the transforma- 

 tion of energy. At the speaking end of the line the energy 

 of motion is transformed into electrical energy, and at the 



