# What is meant by back emf in dc motor?

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Counter-electromotive force (counter EMF, CEMF), also known as back electromotive force (back EMF), is the electromotive force or “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).

## What is back emf in dc motor?

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.

## Why is back EMF 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. … Note that the magnetic field lines begin to collapse as the flow of electricity slows.

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## What is back EMF class 12?

CBSE NCERT Notes Class 12 Physics Electromagnetic Induction. Self-induced Emf is also known as back Emf. Back Emf tries to oppose change in the current.It tries to bring back the current. … In a coil there is increase in the current as a result there is change in the magnetic flux because of that there is induced Emf.

## What is back EMF formula?

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.

## Is back EMF good or bad?

It’s kind of a good thing. Back EMF keeps current from going nuts. Pure resistance is kept low to keep heating down. After you’ve done that, you are relying on back EMF to keep your breakers un-popped and power components un-cratered.

## How do you prevent back EMF?

Back EMF cannot be prevented but it can be controlled. In suppressing the back EMF the objective is to prevent the very high voltages and dissipate the stored energy in a controlled way.

## 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 is an EMF created?

In nature, emf is generated when magnetic field fluctuations occur through a surface. … In an electrical generator, a time-varying magnetic field inside the generator creates an electric field via electromagnetic induction, which creates a voltage difference between the generator terminals.

## How do you increase back EMF?

increasing power of motor is not same as increasing load on motor. if you increase the power of motor its back emf would increase as it will consume more energy. V=IR Increasing power of motor means decreasing its resistance and hence increasing current.

## What is the basic cause of induced emf?

The most basic cause of an induced EMF is change in magnetic flux. … Placing a current carrying coil that is moving constantly in a stable and static magnetic field. This will cause a change in the area vector and hence, EMF will be generated.

## Is there back EMF in AC motors?

This is an example of energy conversion from mechanical to electrical energy and then back to mechanical energy. As the motor is turning, it also acts as a generator and generates a “back emf”. By Lenz’s law, the emf generated by the motor coil will oppose the change that created it.

## What will happen if the back EMF of a DC motor vanishes suddenly?

What will happen if the back emf of a DC motor vanishes suddenly? Explanation: If back emf vanishes suddenly, motor circuit will try to retain back emf by drawing more current from supply. If supplying unit didn’t trip down by this time, excess current in armature may heat up the armature. 3.

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## How do you reduce the back EMF of a dc motor?

To avoid this problem, take the effect of back-EMF into consideration in system design. Motors do have a blowback voltage, a back-EMF that is usually addressed by adding a reverse-biased fast diode, sometimes in addition to a capacitor, across the motor’s supply wires.

## What is the importance of back EMF in DC motor?

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.