Question

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

Answer 1

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 F = qv × 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.