( ( Since ( ( a ( magnetic field ) ) ( is ( produced ( around ( a ( current ( carrying wire ) ) ) ) ) ) ) ) ( , ( ( ( the ( magnetic field ) ) ( around ( ( the coil ) ( of ( wire ( circling ( the compass ) ) ) ) ) ) ) ( ( is ( what ( causes ( the ( compass ( needle ( to ( be deflected ) ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (SBAR (IN Since) (S (NP (DT a) (JJ magnetic) (NN field)) (VP (VBZ is) (VP (VBN produced) (PP (IN around) (NP (DT a) (JJ current) (NN carrying) (NN wire))))))) (, ,) (NP (NP (DT the) (JJ magnetic) (NN field)) (PP (IN around) (NP (NP (DT the) (NN coil)) (PP (IN of) (NP (NP (NN wire)) (VP (VBG circling) (NP (DT the) (NNS compass)))))))) (VP (VBZ is) (SBAR (WHNP (WP what)) (S (VP (VBZ causes) (NP (DT the) (JJ compass) (NN needle) (S (VP (TO to) (VP (VB be) (VP (VBN deflected)))))))))) (. .)))
Since a magnetic field is produced around a current carrying wire, the magnetic field around the coil of wire circling the compass is what causes the compass needle to be deflected.
(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)))) (. .)))