Manual

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33. Ohm’s Law
Build the circuit, press the switch (62) and you will
hear the alarm (78) while the LED (69) turns on at the
same time. Using Ohm’s Law the resistance of each
part could be calculated. If you had a voltmeter and
measured the voltage drop across each component,
you would see that the voltage drop across the LED
(69) and the alarm (78) are similar (around 2V to
2.5V drop across each). According to Ohm’s Law,
R = V÷I which means the internal resistance of the
LED (69) is similar to the internal resistance of the
alarm (78). However, the LED (69) is dim and the
alarm (78) is softer because they each have lower
voltage across them when in series like this circuit.
Each part is designed using Ohm’s Law to perform
best when they have full battery voltage.
34. Visual & Audio Alarm
Build the circuit, press the press switch (61) several
times, the alarm (78) will sound for short intervals. If
you hold the press switch (61), the alarm (78) will start
while the LED (69) is on. 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.