ELECTRIC BELLS



An electric bell is a surprisingly clever device. It works using direct current from a battery, but it makes a hammer move repeatedly back and forth to strike the gong and produce the sound, which tells us, for example, that someone is at the door. Notice that the construction of a typical doorbell. Notice that the hammer is attached to a springy metal strip, and is normally not in contact with the gong. 

  • When someone presses on the bell push, the circuit is completed. Current flows from the battery round through the electromagnetic coil and springy strip, and back to the battery via at point P.
  • The coil is now magnetised and attracts the springy strip. Two things now happen: the hammer strikes the gong and the circuit breaks at point P. 
  • The current stops, the coil is no longer magnetised, and the strip springs back to its original position.
  • Now the circuit is complete again and a current flows once more. The coil is magnetised and attracts the iron again, the hammer strikes the gong, and so on.
  • This process repeats itself for a long as the bell push is depressed.







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