# Question: What Is Back EMF In Motor?

## 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 is Lenz’s Law equation?

According to Lenz’s law, when an electromagnetic field is generated by a change in magnetic flux, the polarity of the induced electromagnetic field produces an induced current whose magnetic field opposes the initial changing magnetic field which produced it. The formula for Lenz law is shown below: ϵ=−N∂ΦB∂t.

## How is motor speed measured?

Motor Speed MeasurementA strobe light (stroboscope) may be used to measure RPM. Some strobe lights have active counters showing the flash rate.Optical tachometers may be used to determine spin rate, however they require something like a propeller attached to the motor which may slow it down.

## Is back EMF good or bad?

Back emf is a measure of energy conversion from electrical to mechanical in an electric motor. If you are able to make it zero no energy conversion to mechanical. … Eb is back emf, I armature current and R armature circuit resistance. So if you want energy conversion back emf is good.

## 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.

## How is back EMF of a motor measured?

If you know your motor, then you know its internal resistance. 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.

## 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.

## What two factors determine the amount of torque developed by a DC motor?

What two factors determine the amount of torque developed by a DC motor? The strength of the magnetic field in the armature, and the strength of the magnetic field in the poles.

## How does back EMF effect a 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.

## What is meant by back EMF?

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.

## What is the advantage of back EMF?

The high value of back emf decreases the armature current. The small magnitude of armature current develops less driving torque, which is equal to the load torque. And the motor will rotate uniformly at the new speed.

## How do you calculate back EMF constant?

Motor velocity constant, back EMF constant = 5,700 rpm/V supplied with 11.1 V will run at a nominal speed of 63,270 rpm (= 5,700 rpm/V × 11.1 V). of the motor/generator. . Sometimes it is expressed in non SI units volts per kilorevolution per minute (V/krpm).

## 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 is self induced emf?

Definition: Self-induced emf is the e.m.f induced in the coil due to the change of flux produced by linking it with its own turns. This phenomenon of self-induced emf can be further understood by the following example given below: Consider a coil having N number of turns as shown in the above figure.

## What is back EMF and its significance?

The significance of Back EMF 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.