Charged Particle at rest in a Solenoid (conceptual question)

[TheSoftAttack]

Homework Statement

There is a solenoid with a magnetic field of a constant magnitude B. In this solenoid is a charged particle, initially at rest, at a certain distance r from the axis of the solenoid. After a certain amount of time, the magnetic field is instantaneously flipped in direction (magnitude remains the same). Will anything happen to the particle as a result of this flip, and if so, describe the trajectory of the particle.

Homework Equations

F = qv x B, where v is initially 0.

The Attempt at a Solution

Obviously, the particle starts at rest, and because of the fact that the particle has a velocity of zero, the magnetic field will not have any force on the particle. Normally, there would be an emf produced by the changing magnetic field of the solenoid as its magnetic field is being flipped, but in this particular case, since the change is instantaneous (or practically instantaneous), I think they want me to neglect the change in the magnetic field over time :/ This would mean that nothing would happen to the particle at all, right? But the way the problem is worded is unsettling to me, because it seems to imply that the particle actually would move, somehow.

I am kind of stuck on this problem, and any help would be greatly appreciated.

 

[Delphi51]

I suspect the idea is to use that Maxwell law that says a changing magnetic field causes an electric field to circulate around it, proportional to the rate of change of the magnetic field. An infinite E field for an infinitesimal time?