# What is the back EMF of a dc motor?

When the armature of a d.c. motor rotates under the influence of the driving torque, the armature conductors move through the magnetic field and hence e.m.f. is induced in them as in a generator. The induced e.m.f. acts in opposite direction to the applied voltage V (Lenz’s law) and in known as back or counter e.m.f.

Thereof, how does back EMF occur?

Counter-electromotive force. The term back electromotive force is also commonly used to refer to the voltage that occurs in electric motors where there is relative motion between the armature and the magnetic field produced by the motor’s field coils, thus also acting as a generator while running as a motor.

What is the back EMF of the 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.

What is EMF how it is produced?

Current produced by the relative motion of coil or magnet is called induced current, set up by an induced electromotive force or EMF. The production of EMF in a coil is called the phenomenon of ELECTROMAGNETIC INDUCTION.

## What is the use of back EMF?

Back EMF is important for DC motors . During starting , the back emf is zero and very large current flows through the motor (limited by armature resistance which itself is very small) , however as the motor picks up speed , the back emf opposes and limit the current to safe value.

## What is back EMF in a DC motor?

When the armature of a d.c. motorrotates under the influence of the driving torque, the armature conductors move through the magnetic field and hence e.m.f. is induced in them as in a generator. The induced e.m.f. acts in opposite direction to the applied voltage V (Lenz’s law) and in known as back or counter e.m.f.

## What causes back EMF in an electric 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.

## What is the back EMF in Transformers?

A changing. magnetic field inside a coil will (by Lenz’s law) induce an EMF in that coil that OPPOSES the. change in current that produced this change in field and therefore in the opposite. direction (opposite sign) to the applied voltage. This EMF is called “back EMF” or vback.

## Is there a back EMF in a generator?

There is no back emf in a generator.This action is observed in a motor only. When a machine is working as a motor it carries current in the armature and that armature is rotating in a magnetic field hence an emf is generated in the armature as given by Faraday’s law and is in opposite direction as per Lenz’s law.

## How is back EMF induced in an electric motor?

But when these currents are induced they will be in a opposite direction with the applied current and since it is in a counter direction therefore it is known as the back EMF. When a armature is moving in a permanent magnetic field than induced current in the coil and this current also produced magnetic field.

## Where DC motor is used?

The series DC motor is an industry workhorse for both high and low power, fixed and variable speed electric drives. Applications range from cheap toys to automotive applications. They are inexpensive to manufacture and are used in variable speed household appliances such as sewing machines and power tools.

## How do you change the direction of a DC motor?

To reverse the motor, you need to change the polarity of the supply voltage to either the field winding or the armature winding, but not both. Generally it is better to reverse the field voltage because the field current is less than the armature current, so your reversing switchgear is more lightweight.

## What is back EMF of synchronous motor?

The only difference is conductors are stationary and flux is rotating. Due to this there is an induced e.m.f. in the stator which according to Lenz’s law opposes the supply voltage. This induced e.m.f. is called back e.m.f. in case of synchronous motor.

## What is the synchronous speed of the motor?

In a motor, synchronous speed is the speed at which the magnetic field rotates. Depending on motor design, the actual mechanical speed may be equivalent (synchronous motor) or slightly smaller (asynchronous motor). The synchronous speed is a function of: The electrical frequency used, typically 60 Hz or 50 Hz.

## Why do we need a starter in DC motor?

In other words, the starter offers resistance to armature current during starting of dc motor only. As the speed of armature/motor build up, armature induced emf also starts building thus reducing the role resistance offered by the starter, hence requiring it to gradually reduce as the motor picks up full speed.

## Why is back EMF used for a DC motor?

When the armature of a d.c. motor rotates under the influence of the driving torque, the armature conductors move through the magnetic field and hence e.m.f. is induced in them as in a generator. The induced e.m.f. acts in opposite direction to the applied voltage V (Lenz’s law) and in known as back or counter e.m.f.

## What is a shunt in a motor?

A shunt DC motor connects the armature and field windings in parallel or shunt with a common D.C. power source. This type of motor has good speed regulation even as the load varies, but does not have the starting torque of a series DC motor.

## What is the back EMF?

The counter-electromotive force (abbreviated counter EMF, or CEMF), also known as the back electromotive force, is the voltage, or electromotive force, that pushes against the current which induces it. For example, the voltage drop across an inductor is due to the induced magnetic field inside the coil.

## What type of starter is used for DC shunt motor?

A 3 point starter is used for starting a DC shunt motor. A 4 point starter is used for starting a DC compound wound motor.

## What is meant by slip in an induction motor?

Slip can be defined as the difference between the flux speed (Ns) and the rotor speed (N). Speed of the rotor of an induction motor is always less than its synchronous speed. It is usually expressed as a percentage of synchronous speed (Ns) and represented by the symbol ‘S’.

## How is the electromotive force generated?

When a magnet is moved into a coil of wire, changing the magnetic field and magnetic flux through the coil, a voltage will be generated in the coil according to Faraday’s Law. The polarity of the induced emf is such that it produces a current whose magnetic field opposes the change that produces it.

## What current flows in the interpole winding?

What current flows in the interpole windings? The DC motor is reversed by reversing the direction of the current in the armature. When the armature current is reversed, the current through the interpole is also reversed. Therefore, the interpole still has the proper polarity to provide automatic commutation.

## What is shaft in DC motor?

The DC, permanent magnet, brushed electric motor is the workhorse of small, powered mechanical systems. Small motors like to spin fast with low torque. The gearing reduces the shaft speed and increases the torque. When the motor leads are connected to a source of DC power, the shaft spins.

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