Left-hand rule, for finding the direction of the mechanical force that acts on a current-carrying conductor in a magnetic field: if the left palm is held so that the outstretched fingers coincide with the direction of the current and the lines of force of the magnetic field enter the palm, then the extended thumb shows the direction of the force acting on the conductor. (It must be borne in mind that the direction of the current is taken to be the direction opposite to the motion of an electron or a negative ion in an electric field.) The left-hand rule gives the direction in which the magnetic part of the Lorentz force acts.