Question

Please explain me right hand thumb rule

Answer 1

The direction of the cross product may be found by application of the right hand rule as follows: The index finger points in the direction of the velocity vector v. The middle finger points in the direction of the magnetic field vector B. The thumb points in the direction of the cross product F.

Answer 2

right hand thumb rule
Imagine you are holding a straight current carrying conductor
the thumb points towards the direction of current
and the the rest of the fingers wrapped around the conductor shows the direction of the magnetic field