Which statement accurately contrasts AC with DC?

Which statement accurately contrasts AC with DC?

• A. AC has fixed polarity and can cause arc blow
• B. AC has no fixed polarity and does not cause arc blow
• C. AC is always smoother than DC
• D. AC cannot reverse direction

Answer: (B)

The fundamental idea here is how polarity and arc behavior differ between alternating current and direct current. With AC, the current reverses direction every half cycle, so there is no fixed polarity throughout welding. With DC, the polarity stays constant, which creates a steady magnetic field around the arc. That steady field can push the arc along the workpiece—arc blow—especially on long or awkward joints. Because AC continually reverses, its magnetic influence tends to cancel over a cycle, making arc blow much less of an issue than with DC. So the statement that AC has no fixed polarity and does not cause arc blow best captures these distinctions. The other options misstate AC’s characteristics: AC does reverse direction, it isn’t inherently smoother than DC, and AC does not have a fixed polarity.

The fundamental idea here is how polarity and arc behavior differ between alternating current and direct current. With AC, the current reverses direction every half cycle, so there is no fixed polarity throughout welding. With DC, the polarity stays constant, which creates a steady magnetic field around the arc. That steady field can push the arc along the workpiece—arc blow—especially on long or awkward joints. Because AC continually reverses, its magnetic influence tends to cancel over a cycle, making arc blow much less of an issue than with DC. So the statement that AC has no fixed polarity and does not cause arc blow best captures these distinctions. The other options misstate AC’s characteristics: AC does reverse direction, it isn’t inherently smoother than DC, and AC does not have a fixed polarity.