A long solenoid has $200$ turns per cm and carries a current of $2.5\, amps$. The magnetic field at its centre is $({\mu _0} = 4\pi \times {10^{ - 7}}\,weber/amp{\rm{ - }}m)$
  • A$3.14 \times {10^{ - 2}}\,weber/{m^2}$
  • B$6.28 \times {10^{ - 2}}\,weber/{m^2}$
  • C$9.42 \times {10^{ - 2}}\,weber/{m^2}$
  • D$12.56 \times {10^{ - 2}}\,weber/\,{m^2}$
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