Data Sheet

-65-
100. Sound Waves
Build the circuit, turn on the switch (62) and you will hear the warning
sounds from the alarm (78), but the lamp (76) is off. The internal
resistance of the alarm (78) limits the current in this circuit preventing
the lamp (76) from lighting. The alarm (78) makes sound by creating
sound waves, much like light waves, but at much longer wavelengths
and much lower frequencies.
Frequency is the inverse of wavelength (frequency = 1/wavelength)
and is measured in Hertz (Hz). The human ear can hear sound waves
between about 20 Hz and 20 kHz (20,000 Hz).
101. Visual and Audio Alarm
Build the circuit shown on the left. In this circuit, the alarm (78) and the
heart LED (69) are connected in parallel, and they are both connected
in series with the lamp (76). This is called series-parallel circuit. This
type of circuit could be used to provide both an audio alarm and a visual
alarm in case the room was too loud to hear the audio alarm.
+
–
+
–
+
–