Where does the electric charge that flows in the
electrical circuits, through the heating filament, or in-and-out
of a capacitor in our previous experiments come from?
Electric charge can be generated by many methods including
electro-magnetic (dynamo), photovoltaic (solar cells) and
electrochemical (batteries and fuel cells) as shown in Fig.1.
High power electrical equipment (or high watt) can produce
more work within the same length of time. Therefore,
sufficient electric energy must be fed to the equipment to
keep it running. In the other word, the power supply must
generate enough charge for the equipment to use.
How do we choose a power supply that could give enough
electricity (or power) for an electric device? Which of the
battery shown in Fig.2 can provide the highest power? Is it
the one with largest size or the one with highest volt?
Fig.2 Primary (disposable) batteries come with various size (AAA-D) but
the same output voltage of 1.5V or with higher voltage of 4.5 - 9 V.
Typically, the voltage indicated on this kind of cells is their
open circuit voltage (OCV). When connected to an external
load, the nominal voltage is somewhat lower than the OCV,
depending on their “specific energy” value. Alkaline and
lithium batteries have a much higher specific energy (0.5 and
1.0 MJ/kg, respectively) making them more suitable for highdrain
devices