# Am I wrong about the right hand grip rule?

The right hand grip rule (also known as right hand screw rule) tells you the direction of a magnetic field due to a current. If you point your thumb in the direction of the current, your fingers will curl in the direction of the magnetic field.

I always thought the same could be applied to the opposite scenario. If there is a moving positive charge in a uniform magnetic field, I thought that the direction of its orbit could be found by pointing your thumb (of your right hand) in the direction of the magnetic field, and your fingers would curl in the direction of the positive charge's orbit.

But suddenly I have noticed that if I firgure out the direction of the Lorentz force, $\mathbf{F}=q\mathbf{v\times B}$, using the other right hand rule for cross products, I get the opposite direction. So I've become very confused.

Is the second paragraph wrong (and hence, have I been wrong about the right-hand grip rule since I left school)? Should it be the left hand you use in that situation?

• Your expression for the magnetic force is dimensionally incorrect. Commented May 15, 2016 at 7:01
• You may be interested in the following physics.stackexchange.com/questions/253457/…
– jim
Commented May 15, 2016 at 8:32