( ( Alternating ( ( current ( Electrical current ) ) ( which ( periodically ( reverses ( ( direction ( , ( usually ( several times ) ) ) ) ( per second ) ) ) ) ) ) ) . )
(ROOT (S (VP (VBG Alternating) (NP (NP (JJ current) (JJ Electrical) (NN current)) (SBAR (WHNP (WDT which)) (S (ADVP (RB periodically)) (VP (VBZ reverses) (NP (NP (NN direction) (, ,) (RB usually) (JJ several) (NNS times)) (PP (IN per) (NP (NN second))))))))) (. .)))
Alternating current Electrical current which periodically reverses direction, usually several times per second.
(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))))))))) (. .)))