Positive and Negative
In DC circuits, the positive pole is usually marked red (or "+") and the negative pole is usually marked black (or "-"), but other color schemes are sometimes used in automotive and telecommunications systems. On a car battery, the positive pole usually has a larger diameter than the negative pole.
In AC systems which are at no point connected to earth (unlike domestic mains wiring where the neutral is commonly earthed at substations and generators) polarity is not important as the two wires alternate polarity many times per second.
Read more about this topic: Electrical Polarity
Famous quotes containing the words positive and/or negative:
“The learner always begins by finding fault, but the scholar sees the positive merit in everything.”
—Georg Wilhelm Friedrich Hegel (1770–1831)
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—Sara Lawrence Lightfoot (20th century)