left-hand rule[′left ¦hand ‚rül]
a mnemonic rule for determining the direction of the mechanical force that acts on a current-carrying conductor in a magnetic field. It may be formulated as follows: If the left palm is held in such a manner that the outstretched fingers follow the direction of the current and the lines of force of the magnetic field pass through the palm, then the thumb indicates the direction of the force acting on the conductor. When using the left-hand rule to find the direction of the force acting on an electron or a negative ion moving in a magnetic field, the fact that the direction of motion of the electron is opposite to the generally accepted conventional direction of an electric current must be taken into account. The rule determines the direction of the magnetic component of the Lorentz force.