Data Sheet

-58-
86. Batteries
Build the circuit to the left and you will see that the heart LED (69) is on.
Now if you turn on any switch, you will see the star LED (70) is on too.
Ever wonder how the batteries in your circuit work? Batteries have three
parts, an anode (–), a cathode (+), and the electrolyte, as shown in the gure
below. When the cathode and anode are hooked up to an electrical circuit,
a chemical reaction occurs in the battery causing a buildup of electrons
at the anode, making the anode negatively charged, and a shortage of
electrons (called holes) in the cathode, making the cathode positively
charged. This results in an electrical difference between the anode and
the cathode. The electrons want to rearrange themselves to get rid of
this difference, but due to the properties of the Electrolyte, the electrons
will not move through the Electrolyte region. So the
only place for the excess of electrons to go is to
the cathode, which causes current to ow in the
circuit. When this happens, conventionally it is said
that “positive” current is owing from the cathode
to the anode (while “negative” current or electrons
ow from anode to cathode).
87. Direction that Current Flows
Build the circuit shown and you will see the heart LED (69) is on. If you
want to turn on the star LED (70), you can turn on the switch (62) and
either press the press switch (61) or touch the reed switch (83) with
the magnet (7).
Based on the discussion on batteries in the previous project, you could
say that current is owing from the “–” terminal of the battery to the “+”
terminal of the battery since electrons are moving that direction. In fact,
some in the industry will refer to this as “electron ow notation”. However,
the more conventional notation for current ow is based on “hole current”.
In electronics, a hole is an electric charge carrier with a positive charge,
equal in magnitude but opposite in polarity to the charge on the electron.
So instead of thinking about electrons moving from the “–” terminal to the
“+” terminal of the battery, you can think of hole current as move from
the “+” terminal to the “–” terminal of the battery. All discussions in this
manual have used the more conventional hole current denition.
1st level
2nd level
1st level
+
–
+
–
+
–
+
–