The magnetic induction at the centre $O$ in the figure shown is
  • A$\frac{{{\mu _0}i}}{4}\left( {\frac{1}{{{R_1}}} - \frac{1}{{{R_2}}}} \right)$
  • B$\frac{{{\mu _0}i}}{4}\left( {\frac{1}{{{R_1}}} + \frac{1}{{{R_2}}}} \right)$
  • C$\frac{{{\mu _0}i}}{4}({R_1} - {R_2})$
  • D$\frac{{{\mu _0}i}}{4}({R_1} + {R_2})$
IIT 1988, Diffcult
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