When current flows through a conducting wire, and an external magnetic field is applied across that flow, the conducting wire experiences a force perpendicular both to that field and to the direction of the current flow (i.e they are mutually perpendicular).
A left hand can be held, as shown in the illustration, so as to represent three mutually orthogonal axes on the thumb, fore finger and middle finger. Learn to use your own two hands to understand the relationship between electricity and magnetism.
Each finger is then assigned to a quantity (mechanical force, magnetic field and electric current). The right and left hand are used for generators and motors respectively.
Fleming’s left-hand rule is used for electric motors, while Fleming’s right-hand rule is used for electric generators.Different hands need to be used for motors and generators because of the differences between cause and effect./National MagLab