Power
A voltage difference is generated by a difference in potential energy between two points. Therefore, to generate a voltage you use a device that can create such an energy difference. Such devices may be mechanical (generators), which convert motion into a potential difference by electromagnetics, photovoltaic (solar cells), or chemical (batteries). Conversely, a voltage difference (and thereby current flow) can be used to produce mechanical movement (motors), light emission (lightbulbs, LEDs), and heat (toasters, Pentium 4 processors).
Power is the amount of work per
time (Joules per
second) and is measured in Watts (unit symbol
W). The equation for calculating power is simply:
P = V * I
No electronic device is 100% efficient (far from it!), and so it will consume power as it performs its task. The power consumed by a device may be calculated using the preceding equation, from the voltage difference across the device and the current flowing through the device. A typical embedded computer may consume a few hundred mW (milliWatts) of power, but it can vary quite considerably. A large and powerful embedded machine may use several tens (or even hundreds) of Watts, while a tiny embedded controller may use just microWatts.
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