$A$ long solenoid carrying a current produces a magnetic field $B$ along its axis. If the number of turns per $cm$ is doubled and the current is made $\left(\frac{1}{3}\right)^{rd}$ of its original value,then the new value of the magnetic field will be:

  • A
    $\frac{B}{3}$
  • B
    $3B$
  • C
    $2B$
  • D
    $\frac{2B}{3}$

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