( Also ( , ( ( ( ( ( ( ( ( the potential ) ( is ( singular ( on ( the ( point charges ) ) ) ) ) ) , ) so ) ( ( the ( equipotential surfaces ) ) ( ( can not ) ( ` ( start ' ) ) ) ) ) and ) ( ( ( ` ( stop ' ) ) ( like ( field lines ) ) ) do ) ) . ) ) )
(ROOT (S (ADVP (RB Also)) (, ,) (S (NP (DT the) (NN potential)) (VP (VBZ is) (NP (NP (NN singular)) (PP (IN on) (NP (DT the) (NN point) (NNS charges)))))) (, ,) (IN so) (S (NP (DT the) (JJ equipotential) (NNS surfaces)) (VP (MD can) (RB not) (VP (`` `) (VB start) ('' ')))) (CC and) (S (NP (NP (`` `) (NN stop) ('' ')) (PP (IN like) (NP (NN field) (NNS lines)))) (VP (VBP do))) (. .)))
Also, the potential is singular on the point charges, so the equipotential surfaces cannot 'start' and 'stop' like field lines do.
(ROOT (S (SBAR (IN Since) (S (NP (DT the) (JJ electric) (NN field) (NNS lines)) (VP (VBP point) (ADVP (RB radially)) (ADVP (RB away) (PP (IN from) (NP (DT the) (NN charge))))))) (, ,) (NP (PRP they)) (VP (VBP are) (ADJP (JJ perpendicular) (S (VP (TO to) (VP (VB equipotential) (NP (NNS lines))))))) (. .)))