
ELECTRICAL SYSTEM 491
contact-breaker points automatically become separated
to interrupt the current flow, which momentarily de-
energizes the system and releases the armature, thereby
allowing the points to close again. This cycle of events
is continuously repeated at a frequency determined by
the characteristics of the flexing diaphragm.
Merely allowing the diaphragm to vibrate in the
manner of a simple buzzer would not, in
itself,
produce
the desired sound from the horn. In practice, a more
effective sound is obtained first by letting the armature
strike the pole piece of the electromagnet, which sets
up a relatively low frequency of vibratio ...