How much electric current is there in an automobile spark plug? — DG, Brooklyn, NY
Without measuring it directly, I would guess that the current passing through a spark plug during a spark is about 10 milliamperes. I base that guess both on a calculation—assuming sensible values for the energy, voltage, and duration of the spark—and on my experience with electric sparks. If I have a chance to measure the current directly—I have the equipment but not the time—I’ll put a more specific value here.