An arc of a circle of radius $R$ subtends an angle $\frac{\pi }{2}$ at the centre. It carries a current $i$. The magnetic field at the centre will be
  • A$\frac{{{\mu _0}i}}{{2R}}$
  • B$\frac{{{\mu _0}i}}{{8R}}$
  • C$\frac{{{\mu _0}i}}{{4R}}$
  • D$\frac{{2{\mu _0}i}}{{5R}}$
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