20.3.2—F = BQv sin θ

A charge Q moving at speed v through magnetic field B feels force magnitude F=BQv sinθ, where θ is the angle between velocity and field.

Use the right-hand rule for a positive charge and reverse direction for a negative charge. The force is zero for parallel motion.

A charge entering perpendicular to B experiences maximum force and follows a circular path if no electric field acts.

Magnetic force depends on velocity direction, not simply speed; a stationary charge feels no magnetic force.