How back emf regulates the armature current in a D.C. Motor? Explain with relevant equations.

5.B] How back emf regulates the armature current in a D.C. Motor? Explain with relevant equations.

When the Armature of D C motor starts rotating and the armature conductor cuts the
magnetic flux, hence an EMF is induced in the Conductor called Back EMF.
The induced emf acts in opposite direction to the applied voltage „V‟(Lenz‟s law) , hence it is
called as back EMF. It is given by

Significance:
The basic Principle of the Back EMF is that E_b α N

When the load suddenly put on the motor, motor tries to slow down. So speed of the motor reduces due to which the back EMF decreases. So the net Voltage( − ) increases and motor draws more armature current.
When the load on the motor decreases, the speed of the motor increases due to which the back EMF increases. So the net Voltage( − ) decreases and motor draws less armature current
Therefore due to the presence of back emf. The d.c. motor acts as a self-regulating machine.
It regulates the flow of armature current i.e., it automatically changes the armature current to meet the load requirement