# Movement of the particle in a magnetic field

This is the numerical question.

A particle having a mass of 0.05 mg carries a charge of $5\times10^{-6}C$. The particle is given an initial horizontal velocity of 5000 m/s, what is the magnitude and direction of the magnetic field that will keep the particle moving in a horizontal direction?

Well I didn't understand this question. what I think is once the charged particle enters the magnetic field whatever magnitude it is it will travel in a circular path. I don't understand why this question is asking for the magnitude of magnetic field so that it will keep moving in horizontal direction.whatever the magnitude is,it should move in a circular path is what i have read but why doesn't it do so?