Engineering Board Exam Reviewer · Alternating Current and Voltage · medium

The voltage v (solid) and the current i (dashed) plotted below have the same frequency. What is their phase relationship? (The time axis is in milliseconds and one cycle is 12 ms.)

1. i lags v by 60°
2. i leads v by 60°
3. i lags v by 120°
4. i leads v by 30°

Answer

A. i lags v by 60°

Solution

i reaches its positive peak later than v does, by t=2 ms. =360°· t/T=360°· 2 ms12 ms=60°. Since i peaks later than, it lags v.

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