The principle of the electromagnet - AC Electric Bell


The electric bell is a small electrical devices that convert electrical energy into mechanical energy in the form of sound.

Educational phase: motivation


Required aids+

  • alternating electric bell
  • battery
  • switch
  • connecting cables
  • AC power


Experiment instructions+

E121_S001 Connect the bell to the battery through the switch.
E121_S002 Switches the button.
E121_S003 The anchor is to attract and make the bell is only one "ding".
E121_S004 Replace the battery with the AC voltage. Stiskeneme button.
E121_S005 The anchor is attracted to the electromagnets periodically.
E121_S006 Periodically mallet strikes the resonator -> bell rings.


After pressing a button that connects the bell circuit, the electromagnet pulls anchor. Anchor oscillates between two poles of the electromagnet core rhythm in the frequency of alternating current, which is powered by the bell. This arrangement creates an electric spark, the current does not break mechanically. Prolonged vibrating armature strikes the bell metal (resonator) and the shock caused by sound effect. Some electric bells have two resonators, which alludes to the mallet, each in one extreme position, and may have a different resonant frequency.

Alternating bell when connected to a DC source does not ring, the anchor is only attracted to one of the electromagnets, thus mallet hits the resonator only once.

Experiment video+

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Application in practice+

It is used as in conventional phones in the house bells for ringing in the school or as an alarm signal at railroad crossings.
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This experiment has been added 14.4.2012 by Jan Krejčí and since then have 29142 visits.
3.6.2014 21:44 © Krejčí Jan