A magnetic compass needle oscillates $30$ times per minute at a place where the dip is $45^o$, and $40$ times per minute where the dip is $30^o$. If $B_1$ and $B_2$ are respectively the total magnetic field due to the earth at the two places, then the ratio $B_1/B_2$ is best given by 

  • [JEE MAIN 2019]
  • A

    $3.6$

  • B

    $1.8$

  • C

    $2.2$

  • D

    $0.7$

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