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

  • A
    $\frac{2 \pi m}{eB}$
  • B
    $\frac{\pi m}{eB}$
  • C
    $\frac{\pi m}{2 eB}$
  • D
    Depends upon the angle between $\vec{v}$ and $\vec{B}$

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