Manual

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54. Efciency Revisited
Build the circuit, press the switch (62), then hold the
press switch (61). Move the magnet (7) towards the
reed switch (83) and you will hear the alarm (78) sound
while the lamp (76) is still off. If you release the press
switch (61) or move the magnet (7), the alarm (78) will
turn off. This circuit shows that the lamp (76) is not very
efcient because even though current is owing through
the lamp (76), meaning there is input power, it does not
light, meaning no output power.
55. Battery Power
Build the circuit, press the switch (62), then hold the
press switch (61). Move the magnet (7) towards the reed
switch (83) and you will hear the alarm (78) sound very
faintly while the bi-directional LED (71) turns on blue. If
you release the press switch (61), or move the magnet
(7) away, the alarm (78) and bi-directional LED (71) will
turn off.
Batteries have a cathode (+ side) and anode (– side) and
are designed to have a build up of electrons in the anode.
When you turn on all the switches in this circuit, it closes
the circuit which allows the build up of electrons to ow
out of the anode enabling current to ow through the
circuit.