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In an AC circuit the voltage and current are v = 5*sin(100*pi*t - pi/6) and i = 4*sin(100*pi*t + pi/6). Which statement about the phase relationship is correct?

1. Voltage leads the current by 30 deg
2. Current leads the voltage by 30 deg
3. Current leads the voltage by 60 deg
4. Voltage leads the current by 60 deg

Correct answer: Current leads the voltage by 60 deg

Solution

Phase of current = +pi/6 = +30 deg; phase of voltage = -pi/6 = -30 deg. The current's phase is ahead of the voltage's by (+30) - (-30) = 60 deg. Hence the current leads the voltage by 60 deg.

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