# What is the role of back EMF in 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.

Subsequently, one may also ask, 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.

What is meant by motor effect?

The motor effect is the term used when a current-carrying wire in the presence of a magnetic field experiences a force. A simple experimental demonstration will show you that this is true. Place a wire that is connected to a power pack in between the poles of a horseshoe magnet.

What is the EMF generator?

AC-Circuits > AC (Alternating Current) Generators. An Electrical Generator is a device that produces an Electromotive Force (e.m.f.) by changing the number of Magnetic Flux Lines (Lines of Force), Φ, passing through a Wire Coil. Figure 1 is one type of Generators.

## What is the back EMF?

Counter-electromotive force (abbreviated counter EMF or simply CEMF), also known as back electromotive force (or back EMF), is the electromotive force or “voltage” that opposes the change in current which induced it.

## What is the role of back EMF?

The significance is that it determines the operating state of a DC machine. A DC machine working as a motor will have its counter emf always less than the supply voltage. The difference would depend on amount of mechanical load tied to the motor. As a result, current would flow into the machine.

## What is back EMF and what does it do?

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 a Lenz law?

Lenz’s law is a common way to understand how electromagnetic circuits obey Newton’s third law and the conservation of energy. Lenz’s law is named after Heinrich Lenz, and it says: An induced electromotive force (emf) always gives rise to a current whose magnetic field opposes the change in original magnetic flux.

## How back EMF is generated?

Back EMF always acts to reduce the changing magnetic field through the coils. It does so by generating a voltage which opposes the supply voltage, thus reducing the current. In ideal DC motor where R=0 and L=0, and RPM is constant with no load, back EMF will be exactly the same as supply voltage.

## 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.

## How is a back EMF produced in a 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.

## What is motor constant?

Motor Constant is a figure of merit used to compare the relative efficiencies and output. power capabilities of different motors. Km defines the ability of the motor to transform electrical power to mechanical power. Motor Constant is calculated by the following equation (in English units):

## 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.

## 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 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.

## 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 a single phase induction motor is not self starting?

Rotating magnetic field, there are minimum two phases required. But in the case of single phase induction motor, there is a single phase. Hence, not self starting. When stator winding of a Single Phase Induction Motor is connected to a sinusoidally alternating voltage source, the stator flux alternates in a space.

## 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 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.

## 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’.

## 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.