The resistances of three parts of a circular loop are as shown in the figure. The magnetic field at the centre $O$ is :-
  • A$\frac{{{\mu _0}I}}{{6a}}$
  • B$\frac{{{\mu _0}I}}{{3a}}$
  • C$\frac{2}{3}\frac{{{\mu _0}I}}{a}$
  • D
    Zero
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