question_answer

A positive charge 'q' of mass 'm' is moving along the +x axis. We wish to apply a uniform magnetic field B for time \[\Delta \,t\] so that the charge reverses its direction crossing the y axis at a distance d. Then:

A) \[B=\frac{mv}{qd}\] and \[\Delta t=\frac{\pi d}{v}\]

B) \[B=\frac{mv}{2qd}\]   and \[\Delta t=\frac{\pi d}{2v}\]

C) \[B=\frac{2mv}{qd}\] and \[\Delta t=\frac{\pi d}{2v}\]

D) \[B=\frac{2mv}{qd}\] and \[\Delta t=\frac{\pi d}{v}\]