( ( ( A flow ) ( of ( electricity ( which ( ( ( ( ( ( ( reaches ( ( a maximum ) ( in ( one direction ) ) ) ) , ) ( decreases ( to zero ) ) ) , ) ( then ( reverses itself ) ) ) and ) ( reaches ( ( ( a maximum ) ( in ( ( ( the ( opposite direction ) ) and ) ( this cycle ) ) ) ) ( ( is continuously ) repeated ) ) ) ) ) ) ) ) ( ( is ( alternating current ) ) . ) )
(ROOT (S (NP (NP (DT A) (NN flow)) (PP (IN of) (NP (NP (NN electricity)) (SBAR (WHNP (WDT which)) (S (VP (VP (VBZ reaches) (NP (NP (DT a) (NN maximum)) (PP (IN in) (NP (CD one) (NN direction))))) (, ,) (VP (VBZ decreases) (PP (TO to) (NP (CD zero)))) (, ,) (VP (ADVP (RB then)) (VBZ reverses) (NP (PRP itself))) (CC and) (VP (VBZ reaches) (SBAR (S (NP (NP (DT a) (NN maximum)) (PP (IN in) (NP (NP (DT the) (JJ opposite) (NN direction)) (CC and) (NP (DT this) (NN cycle))))) (VP (VBZ is) (ADVP (RB continuously)) (VP (VBN repeated)))))))))))) (VP (VBZ is) (VP (VBG alternating) (ADJP (JJ current)))) (. .)))
A flow of electricity which reaches a maximum in one direction, decreases to zero, then reverses itself and reaches a maximum in the opposite direction and this cycle is continuously repeated is alternating current.
(ROOT (S (NP (VBG Alternating) (NN current)) (VP (VBZ is) (NP (NP (DT the) (NN term)) (PP (IN for) (NP (JJ electric) (NN current))) (SBAR (WHNP (WDT that)) (S (VP (VBZ keeps) (S (VP (VBG reversing) (NP (NN direction))))))))) (. .)))