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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 the purpose of back emf?

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 is the back emf of a DC motor?

back EMF in Electrical Engineering

Back EMF is the system in the coil of an electric motor that opposes the current flowing through the coil, when the armature rotates. When the speed varies, the winding characteristics may fluctuate, resulting in variation of back EMF.

## What is the difference between emf and back emf?

If an open coil is subjected to a variable magnetic field, at the ends of the coil a potential difference is induced which is called induced emf. If a coil is connected to an emf source and switched on, the rising current will produced an variable magnetic field which in turn produces an emf. It is called back emf.

## What should happen if there is no back emf?

If there is no back end then large current flows in starting of motors because initial speed is zero and back emf is zero thus winding gets damaged for this purpose only we use starters for all motors. motor will not start. when the motor runs,there has to be back emf.

## Why back emf is less than applied voltage?

Back EMF is less than the applied voltage because of the resistance of the armature winding. In the above circuit the Back emf can be written as, Therefore, Now in the above equation if the value of current is negative then back emf can be higher than the applied voltage, which is the case for the generators.

## What is back emf equation?

The back emf is calculated based on the difference between the supplied voltage and the loss from the current through the resistance. The power from each device is calculated from one of the power formulas based on the given information. The back emf is ϵi=ϵS−I(Rf+REa)=120V−(10A)(2.0Ω)=100V.

## What is back emf constant?

back electromotive force constant (=back EMF constant)

Back electromotive force is the voltage generated at both ends of a winding due to changes in flux linkage in a shaft motor operation. Since the back electromotive force is proportional to the moving speed, it is a constant. The unit is [V/m/s].

## Can back emf be used?

In motor control and robotics, back-EMF often refers most specifically to actually using the voltage generated by a spinning motor to infer the speed of the motor’s rotation, for use in better controlling the motor in specific ways.

## When the value of back emf in a DC motor is maximum?

So, with the increase of the speed of the motor the back emf produced will also increase and with the decrease of the speed of the motor the back emf will also decrease. So, we can say that the back emf in a DC motor will be maximum when the motor has picked the maximum speed.

## What will happen if back emf is equal to original emf?

A2A: If it was equal, then nothing drives the current, but that can’t happen. The inductor voltage is, E=L*di/dt. It is proportional to the Change in current (di/dt). As the current changes, the self-induced EMF opposes the applied voltage change.

## What happens if motor back emf is 0?

So, if back emf is zero that means which tells us that either speed of the motor or field flux or both are zero. In other words, the motor is standstill because field flux is required for creating torque for rotation. So, if E=0, the supplied voltage equals to voltage drop against armature resistance.