Electro Motive Force (EMF) In DC Motor

The Electro Motive Force (EMF) generated in a DC motor:

When the motor is connected to the power supply, the armature of the motor starts rotating in the magnetic field due to the force, then the armature or conductor cuts the magnetic field lines of the main field, causing the Electro Motive Force (EMF) in the motor armature to be used in the direction used. Opposite to voltage, it is called anti- Electro Motive Force (EMF) due to its opposite direction to the voltage used. The voltage supplied to the motor must be high enough to eliminate the effect of the opposing Electro Motive Force (EMF).

With the following formula, we can show the opposing electrical carrying force generated in the motor.
Because

Vb=Eb+IaRa

Where at-

V= is the value of applied voltage used in volts

Eb= Back Electro Motive Force (EMF) in volt

Ra= Resistance of Armature in Ohm

IaRa= Voltage drop in armature

Ia=(V-Eb)/Ra

Or

Eb=V-IaRa Volt

This back Electro Motive Force (EMF) depends on the quantity of flux(Ø) and the speed (N) of the motor.
The time taken in a full cycle is 1/N minute Or  60/N sec

Hence 
Eb=KØN volt

K= The value is a constant whose value 

K=PZ/A

Here

Z= Number of conductor in armature

P= Number of poles

A= Number of parallel paths in the armature

N=  Armature round in one minute (RPM)

Hence

Eb=(ØNPZ)/60A Volt

The value of the opposing Electro Motive Force (EMF) also depends on the speed of the armature. If the speed of the armature of the motor is high, then the opposing electrical carrying force will also be higher, but the armature current will be less. If the speed of the motor is low then the power will also be low and more current will flow in the armature, which will cause more turbulence.