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Military aircraft use 400-Hz AC power because equipment can be built lighter at that frequency. How long does one complete cycle of this power take?
A2.50 ms
B4.00 ms
C0.40 ms
D25.0 ms
Answer & Solution
Correct answer: A. 2.50 ms
1. The period of a wave is the reciprocal of its frequency: T = 1/f.
2. Substitute: T = 1 / 400 Hz.
3. Divide: T = 0.00250 s.
4. Convert to milliseconds: T = 2.50 ms.
5. 25.0 ms is the trap of a one-place decimal slip; it is actually the period of ordinary 40-Hz power, not 400-Hz.
_Source: OpenStax College Physics (CC BY 4.0), Ch 20 "Electric Current, Resistance, and Ohm's Law", section 20.5 Alternating Current versus Direct Current_
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