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GCSE Physics · key term
A potential difference whose polarity remains in one direction, even if its magnitude changes.
Used by OCR
Specification P8.2h · Paper 2 (Foundation), Paper 4 (Higher)
Revise: AC vs DCWith a direct voltage (d.c.), the polarity stays the same: the same terminal remains positive relative to the other. A cell or battery is a familiar source of d.c. In a complete circuit, this drives conventional current in one direction. The size of a direct voltage may change, but it does not reverse polarity.
Paper 1, Paper 2
An electrical supply that maintains the same polarity, so current in a connected circuit flows in one direction.
Describe voltage, not just the shape of a graph: d.c. keeps the same polarity, whereas a.c. repeatedly reverses polarity.
Do not say that all d.c. must have a perfectly constant value. Its magnitude can vary provided its polarity does not reverse.
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A cell or battery provides a direct voltage: its two terminals keep the same polarity. When it is connected into a complete circuit, this drives a current in one direction. On a graph of potential difference against time, an ideal steady direct supply is represented by a horizontal line on one side of zero.