( ( Just ( as ( we ( ( ( described ( the ( electric field ) ) ) ( around ( a ( charged object ) ) ) ) ( by ( field lines ) ) ) ) ) ) ( , ( we ( ( ( can also ) ( ( describe ( the ( electric ( potential pictorially ) ) ) ) ( with ( ( equipotential surfaces ) ( -LRB- ( ( contour plots ) -RRB- ) ) ) ) ) ) . ) ) ) )
(ROOT (S (SBAR (RB Just) (IN as) (S (NP (PRP we)) (VP (VBD described) (NP (DT the) (JJ electric) (NN field)) (PP (IN around) (NP (DT a) (JJ charged) (NN object))) (PP (IN by) (NP (NN field) (NNS lines)))))) (, ,) (NP (PRP we)) (VP (MD can) (ADVP (RB also)) (VP (VB describe) (NP (DT the) (JJ electric) (JJ potential) (NN pictorially)) (PP (IN with) (NP (NP (JJ equipotential) (NNS surfaces)) (PRN (-LRB- -LRB-) (NP (NN contour) (NNS plots)) (-RRB- -RRB-)))))) (. .)))
Just as we described the electric field around a charged object by field lines, we can also describe the electric potential pictorially with equipotential surfaces (contour plots).
(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))))))) (. .)))