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How do direct current (DC) and alternating current (AC) differ over time?
ADC is constant over time; AC alternates smoothly back and forth over time
BDC alternates smoothly over time; AC is constant over time
CBoth DC and AC are constant over time but at different voltages
DBoth DC and AC alternate over time but at different frequencies always
Answer & Solution
Correct answer: A. DC is constant over time; AC alternates smoothly back and forth over time
1. Direct current is described as flowing constantly in a single direction over time.
2. Alternating current is described as reversing direction back and forth at regular intervals, smoothly.
3. Combining these two facts rules out any option that swaps which one is constant.
4. Only the option pairing DC with constant and AC with smoothly alternating matches both stated facts.
_Source: OpenStax Physics (CC BY 4.0), Ch 19 "Electrical Circuits", section 19.1 Ohm's law_
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