Which one of the following statements most accurately reflects the nature of ac power? A. The current in an ac circuit flows in one direction, but changes value periodically B. The current in an ac circuit flows in one direction at a steady level C. The current in an ac circuit changes direction periodically D. The current in an ac circuit flows in two directions at the same time E. None of the above

The correct answer is: D. The current in an ac circuit flows in two directions at the same time.

An alternating current (AC) is an electric current that reverses its direction periodically. The current in an AC circuit flows in two directions at the same time, and the direction of the current changes periodically. The frequency of the AC current is the number of times per second that the current reverses its direction. The frequency of AC current in the United States is 60 Hz, which means that the current reverses its direction 60 times per second.

Option A is incorrect because the current in an AC circuit does not flow in one direction, but changes value periodically. Option B is incorrect because the current in an AC circuit does not flow in one direction at a steady level, but changes value periodically. Option C is incorrect because the current in an AC circuit does not change direction periodically, but flows in two directions at the same time. Option E is incorrect because the statement in option D most accurately reflects the nature of AC power.