- Point your index finger (and your middle finger) along the direction of motion of the charge v. For a current carrying wire this would be along the direction of positive current flow.
- Rotate your middle finger away from your index finger by the angle q between v and B.
- Pivot your wrist about the direction of v until your middle finger is pointing along the direction of the magnetic field B.
- Hold your thumb perpendicular to the plane formed by both your index finger and middle finger.
- Your thumb will then point in the direction of the force F if the charge q is positive. For q < 0, the direction of the force is opposite your thumb - alternately you could use your left hand for negative charges.
