206 



GENERAL SCIENCE 



The electromagnet is used in electric bells, telegraph 

 instruments, the electric crane, and many other appliances. 



The Electric Bell. A sim- 

 ple application of the elec- 

 tromagnet is the electric bell 

 (Figure 180) . When the elec- 

 tric circuit is closed at A, 

 the current flows through the 

 coils of the electromagnet F. 

 The magnet attracts the 

 hammer or armature, causing 

 it to strike the bell. At the 

 same time the circuit is broken 



Dia B r e r f the El6CtriC at G and the magnet is de- 

 magnetized. The hammer is 



thrown back by the spring which supports it. This 

 closes the circuit again and the operation is repeated. 

 So rapidly does this opening and closing of the circuit 

 take place that if the bell is removed, the hammer will 

 produce a buzzing 

 noise. 



The Telegraph. - 

 In this instrument, 

 which is another ap- 

 plication of the elec- 



FIG. 180. 



FIG. 181. Diagram of Telegraph Circuit. 



tromagnet, the earth 

 is used instead of a 

 second wire. When the key K (Figure 181) is closed, 

 the circuit is complete, and the electromagnet A attracts 

 the sounder B and holds it as long as the key is closed. 

 When the circuit is broken at K, the sounder is pulled 

 away from the magnet by a spring at C. A short 

 closing of the key is called a dot, a longer time a dash. 



