Fleming's left-hand rule tells you the direction of the force on a current-carrying conductor in a magnetic field. Hold the thumb, first finger and second finger of your left hand at right angles to each other. The rule works when the field, the current and the force are mutually perpendicular.
- The first finger points in the direction of the magnetic field, from north to south.
- The second finger points in the direction of the conventional current, from positive to negative.
- The thumb then shows the direction of the force, which is the direction the conductor tends to move.
For example, suppose the field points from left to right and the current in a horizontal wire flows away from you. The rule gives a force that acts downwards. If the current is reversed, the force acts upwards. If the field is reversed instead, the force also acts upwards.
