When a particle of charge q is projected with uniform speed u along x - axis of the Cartesian coordinate system (^i,^j,^k) in the presence of a magnetic field of induction →B, the force on q is →F=qu→B2^j and when the particle is projected along y - axis with same speed, the force →F=qu→B2(−^i+√3^k). The magnetic field →B is