question_answer

A particle of mass m and charge q moves with a constant velocity v along the positive x-direction. It enters a region containing a uniform magnetic field B directed along the negative z-direction, extending from \[x=a\] to \[~x=b\]. The minimum value of v required so that the particle can just enter the region x > b is

A) \[\frac{qbB}{m}\]         

B) \[\frac{q(b-a)B}{m}\]

C) \[\frac{qaB}{m}\]         

D) \[\frac{q(b+a)B}{2m}\]