An electron is projected with velocity $\vec v$ in a uniform magnetic field $\vec B$ . The angle $\theta$  between $\vec v$ and $\vec B$  lines between $0^o$ and $\frac{\pi}{2}$ . It velocity $\vec v$ vector returns to its initial  value in time interval of 

  • A

    $\frac{2 \, \pi m}{eB}$

  • B

    $\frac{ \pi m}{eB}$

  • C

    $\frac{ \pi m}{2\,eB}$

  • D

    Depends upon angle between $\vec v$ and $\vec B$

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