Back emf is very significant in the working of a dc motor. The presence of back emf makes the d.c. motor a self-regulating machine i.e., it makes the motor to draw as much armature current as is just sufficient to develop the torque required by the load.

## What is back emf of dc motor and what is its function in dc motor?

When the armature of the DC motor rotates under the influence of driving torque, the armature of the conductors moves through a magnetic field inducing an emf in them. The induced emf **is in the opposite direction to the applied voltage** and is known as the back emf.

## What is meant by back emf?

Counter-electromotive force (counter EMF, CEMF), also known as back electromotive force (back EMF), is **the electromotive force (voltage) that opposes the change in current which induced it**. CEMF is the EMF caused by magnetic induction (see Faraday’s law of induction, electromagnetic induction, Lenz’s law).

## Is back emf AC or DC?

**Back EMF can have either a sinusoidal (AC) or a trapezoidal (DC) waveform**. The shape of the back EMF is important, as it determines the type of drive current and commutation method that should be used for the motor.

## What will happen if the back emf in the motor absent?

If back emf of a dc motor vanishes suddenly, **motor circuit will try to retain back emf by drawing more current from supply**. As the back emf vanishes zero, the whole supply voltage appears across armature and heavy current flows.

## What is back emf equation of DC motor?

As the armature rotates, a voltage is generated in its coils. In the case of a generator, the emf of rotation is called the Generated emf or Armature emf and is denoted as Er = Eg. In the case of a motor, the emf of rotation is known as Back emf or Counter emf and represented as **Er = Eb**.

## Why does back emf occur?

A motor has coils turning inside magnetic fields, and a coil turning inside a magnetic field induces an emf. This emf, known as the back emf, **acts against the applied voltage that’s causing the motor to spin in the first place**, and reduces the current flowing through the coils of the motor.

## What does back EMF depend on?

The back EMF depends, of course, on **the speed of the motor** — the change in magnetic flux that generates it increases with motor speed — so that as the motor begins to turn, the back EMF grows until the motor has reached its maximum speed, at which point the back EMF stays at its maximum value.

## How do you measure back EMF?

You can measure the voltage and current apllied to the motor, and **subtract the I*R from the voltage applied**, and voila you get your back EMF.

## How the back EMF or counter emf is produced?

This back EMF is produced as **a result of Lenz’s Law**, which says that in a circuit with an induced EMF caused by a change in a magnetic field, the induced EMF causes a current to flow in the direction that opposes the change in flux.