( ( 28 ( The ( magnetic field ) ) ) ( ( does ( ( no work ) ( on ( a ( moving charge ) ) ) ) ) . ) )
(ROOT (S (NP (NP (CD 28)) (NP (DT The) (JJ magnetic) (NN field))) (VP (VBZ does) (NP (NP (DT no) (NN work)) (PP (IN on) (NP (DT a) (VBG moving) (NN charge))))) (. .)))
28 The magnetic field does no work on a moving charge.
(ROOT (S (NP (NNP Work)) (VP (VBZ is) (SBAR (WHNP (WP what)) (S (NP (PRP it)) (VP (VBZ is) (VP (VBN called) (SBAR (WHADVP (WRB when)) (S (NP (DT a) (NN charge)) (VP (VBZ moves) (PP (IN against) (NP (DT a) (NN field))))))))))) (. .)))