A particle moves in a region having a uniform magnetic field and a parallel, uniform electric field. At some instant, the velocity of the particle is perpendicular to the field direction. The path of the particle will be

Magnetic force will act in perpendicular direction of the magnetic field and velocity, and it will cause the circular motion of the particle. While, electric force will act in the direction of fields, and it will accelerate the particle in electric field direction. So, the path of the particle will be helical with increasing pitch length.