1) Alternant 2) Antiphonal 3) Cyclical 4) Irregular 5) Responsive 1) First one and then the other 2) Occurring by turns 3) Reversing direction 
• (p. pr. & vb. n.) of Alternate
pertaining to a periodic quantity of zero mean value
[adj] - (electricity) of a current that reverses direction at regular intervals
alternating 1. To occur in a successive manner: day alternating with night. 2. To act or proceed by turns: The students were alternating at the computers. 3. To pass back and forth from one state, action, or place to another: alternating between happiness and depression. 4. In electricity: to reverse directions at regular intervals in a circuit.
adjective (of a current) reversing direction; `alternating current`