A straight wire of length $({\pi ^2})$ $metre$ is carrying a current of $2\,A$ and the magnetic field due to it is measured at a point distant $1\, cm$ from it. If the wire is to be bent into a circle and is to carry the same current as before, the ratio of the magnetic field at its centre to that obtained in the first case would be
  • A$50:1$
  • B$1:50$
  • C$100:1$
  • D$1:100$
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