( ( ( The ( magnetic ( field lines ) ) ) ( of ( a ( straight ( current-carrying wire ) ) ) ) ) ( ( ( form ( concentric circles ) ) ( around ( the wire ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (JJ magnetic) (NN field) (NNS lines)) (PP (IN of) (NP (DT a) (JJ straight) (JJ current-carrying) (NN wire)))) (VP (VBP form) (NP (JJ concentric) (NNS circles)) (PP (IN around) (NP (DT the) (NN wire)))) (. .)))
The magnetic field lines of a straight current-carrying wire form concentric circles around the wire.
(ROOT (S (NP (DT The) (JJ magnetic) (NN field)) (VP (VBD produced) (PP (IN by) (NP (NP (DT a) (NN current)) (PP (IN in) (NP (DT a) (NN wire) (NNS moves))))) (PP (IN in) (NP (JJ concentric) (NNS circles)))) (. .)))