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In an AC circuit, an ideal capacitor C is in series with a resistor R2, and this branch carries the same current. Considering the voltages across the capacitor (V_C) and across R2 (V_R2) in that series branch, the phase difference between V_C and V_R2 is

1. 90 deg
2. 0 deg
3. 180 deg
4. 45 deg

Correct answer: 90 deg

Solution

For elements in series the current is the common reference. Across a resistor, voltage is in phase with the current (phase 0). Across a capacitor, the voltage lags the current by 90 deg. Therefore V_R2 (in phase with I) and V_C (90 deg behind I) differ in phase by 90 deg.

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