The radius of the circular path or helical path followed by the test charge qo moving in magnetic field B with some velocity v is

The circular motion of charged particle will be due to component of velocity v perpendicular to magnetic field, i.e., v sinθ∴ m(vsin⁡θ)2r=q0(vsin⁡θ)Bor r=m(vsin⁡θ)q0B