Fig. 40
In the case of the buzzer, by changing the length of the armature or by weighting it, we may change the time of its vibrations and its tone. The connections between battery push button and bell form a complete circuit. In [Fig. 40] B represents a battery, usually of dry cells, B' represents the bell, and P represents the push button. The electric circuit is "open," (that is, there is a break in the conductor) at P until some one "pushes the button," that is, simply pushes against a spring so as to cause a piece of metal to bridge the gap in the conductor. Then we say the circuit is "closed."
Fig. 41
