ACROSS \[AB\] \[{{i}_{1}}{{R}_{1}}={{i}_{2}}{{R}_{2}}\Rightarrow {{i}_{1}}{{l}_{2}}={{i}_{2}}{{l}_{2}}\] \[\left( \because \ R=\rho \frac{l}{A} \right)\] Also \[{{B}_{1}}=\frac{{{\mu }_{o}}}{4\pi }\times \frac{{{i}_{1}}{{l}_{1}}}{{{r}^{2}}}\] and \[{{B}_{2}}=\frac{{{\mu }_{o}}}{4\pi }\times \frac{{{i}_{2}}{{l}_{2}}}{{{r}^{2}}}\] (\[\because \ l=r\theta \]) \[\therefore \,\frac{{{B}_{2}}}{{{B}_{1}}}=\frac{{{i}_{1}}{{l}_{1}}}{{{i}_{2}}{{l}_{2}}}=1\] Hence, two FIELD induction?s are equal but of opposite direction. So, resultant magnetic induction at the centre is zero and is independent of\[\theta \].