what is direction of force acting on charged particle q,moving with velocity v in uniform mg. field?

Magnetic fields exert forces on other moving charge.  The force a magnetic field exerts on a charge q moving with velocity v is called the Lorentz Force. 
It is given by = q× B.
(The SI unit of B is Ns/(Cm) = T(Tesla)

The force F is perpendicular to the direction of the magnetic field B. 
It also is perpendicular to the direction of the velocity v. 
F is perpendicular to the plane that contains both v and B.

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