Uniform magnetic fields of different strengths $\left( {{B_1}} \right.$ and $\left. {{B_2}} \right)$, both normal to the plane of the paper exist as shown in the figure. A charged particle of mass m and charge q, at the interface at an instant, moves into the region 2 with velocity v and returns to the interface. It continues to move into region 1 and finally reaches the interface. What is the displacement of the particle during this movement along the interface ?