right hand rule

Meaning: The right hand rule gives the direction of a cross product. For the magnetic force on a moving positive charge, point your fingers along the velocity v, curl them toward the field B, and your thumb points along the force F. For a negative charge, the force is opposite. The force is perpendicular to both v and B, so it does no work. A second use: for a straight current-carrying wire, point the thumb along the conventional current and the fingers curl in the direction of the circular field lines.

Equation: F = qvB sinθ, where F is the force (N), q is the charge (C), v is the speed (m/s), B is the magnetic field (T), and θ is the angle between v and B.

On the MCAT: Expect questions on which way a proton, electron, or wire segment is deflected, or how a charge curves (qvB = mv²/r when v ⟂ B), as in mass spectrometers. Parallel wires with currents in the same direction attract.

Common confusion: Forgetting to reverse the result for an electron; the rule as stated gives the force on a positive charge. Also, the force is not along v or B, and it is zero when v is parallel or antiparallel to B because sinθ = 0.