What is the definition of alternating potential difference?Watch this thread
So its different from DC where one conductor is always more positive than the other.
The most usual frequency for AC power is 50Hz in the UK though it could be 60Hz in some other countries. Aircraft sometimes run on 300Hz power afaik and theres some electrified railways running at 16Hz
All exam boards will accept the following answer on an exam:
"Flow of electric charge that periodically reverses over time"