Working Principle of D.C. Motor An electric motor is a machine which converts electric energy into mechanical energy. It works on the principle of Lorentz Law, which states that ‘the current carrying conductor placed in a magnetic and electric field, experience a force’, whose direction is given by Fleming’s Left-Hand rule and whose magnitude is given by F = BIl Newton. Constructionally, there is no difference between a dc generator and dc motor. In figure above, a part of motor is shown. When its field magnets are excited and its armature conductors are supplied with current from the supply mains, they experience a force tending to rotate the armature. Armature conductors under N-pole are assumed to carry current downwards (crossed), and those under S-pole are assumed to carry current upwards (dots). By applying Fleming’s Left-Hand Rule, the direction of the force on each conductor can be found. It is shown by small arrows placed above each conductor. It will be seen that each conductor experiences a force F which tends to rotate the armature in anti-clockwise direction. These forces collectively produce a driving torque which sets the armature rotating.
