A straight conductor of length $L$ carrying current $I$ in a uniform magnetic field $\vec{B}$ experiences force $\vec{F} = I\vec{L} \times \vec{B}$. Magnitude: $F = BIL\sin\theta$ where $\theta$ is the angle between the wire and $\vec{B}$. Maximum force when $\theta = 90°$ (wire perpendicular to field). Zero force when $\theta = 0°$ or $180°$ (wire parallel to field). Direction: right-hand rule or Fleming's left-hand rule (FBI rule: First finger = Field, seCond = Current, thuMb = Motion/Force).