The difference between A.C and D.C. power
Some years ago I was a trade examiner in the R.A.F., and asked a young lad the same question.
He rapidly responded, 'That's easy - Direct current goes directly to the switch and on to the component by the wire. The alternating current is directed around the aircraft structure before it reaches the switch or component.'
I always recall this when I hear the question. Thanks for the reminder.