Draw a labelled circuit diagram of a simple electric motor and explain its working. In what way these simple electric motors are different from commercial motors?

Explanation

The circuit diagram of a simple electric motor is shown below

Working
(i) Let coil ABCD be in horozontal position. When the key is switched on, the current flows in direction DCBA and then leaves through the brushes `B_(2)` via ring `R_(2)`
(ii) Applying Fleming's left -hand no force act on arm BC and AD as they are parallel to magnetic field, arm AB experiences a forec in downward direction and arm CD experinces and equal force in upward direction. A torque on the coil and it rotates in anti- clockwise direction.
(iii) while rotating, the coil reaches the varticl position, brushes loose contant with the rings and current stops flowing. But the coil does not stop due to inertia of motion.
(iv) When the coil passes the vertical position, the rings automatically change their positions and come in contant with opposite brushes.
(v) This reverses the direction of current through the coil but the direction of current on right-hand side reamain same.
(vi) So, the force on right hand side is always upward and a force on left-hand side is always in downward direction. Thus, the coil continues to anti-aclockwise direction.
A commercial electric motor is one which uses the following
(a) An electromagnet in place permanent magnet.
(ii) Large number of turns conducting wire in current carrying coil.
(iii) A soft iron core on which the coil is wound. The combination of soft iron core and coil is an armature. It enchances the power of motor.
Thus, commercial electric motors do not use permanent magnet to rotate the armature because permanent magnets are weak and do not produce strong magnetic field in the region