Manual

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44. Power
Build the circuit, move the magnet (7) towards the
reed switch (83), the alarm (78) will start in a low
volume while the LED (69) turns on. If you move the
magnet (7) away, the alarm (78) and LED (69) will
turn off. Power is dened as voltage times current
and is measured in Watts. In Project 33 we saw that
the voltage drops across the LED (69) and alarm (78)
in series were similar, and since the current through
both components is the same, this means the power
input to each component is roughly the same.
45. Efciency
Build the circuit, press the switch (62), the alarm (78)
will sound, the bi-directional LED (71) turns on red. Install
the bi-directional LED (71) in the reverse direction, then
press the switch (62), the bi-directional LED (71) will
turn on blue and the alarm will sound very faintly.
Electronic Efciency is dened as the Useful Power Output
divided by the Total Power Input. Although the alarm (78)
sound was softer, the LED (71) is still pretty bright. This
shows that the LED (71) is a little more efcient because
for the same input power (as discussed in the previous
project) the output power (the light intensity) is still high.
Red Light
Blue Light