Short-Question

# Why the emf generated in the armature of a DC motor is called the back emf?

## Why the emf generated in the armature of a DC motor is called the back emf?

When the armature of a DC Motor rotates, then the current-carrying armature windings move through the magnetic field. So that an emf is induced and the emf which is induced in the armature winding of the DC motor is called Back Emf.

Does DC give off emf?

DC electricity produces static electric and magnetic fields, but these fields have very different properties from AC Electric Magnetic Fields (EMF*). Since DC electricity does not vary over time and is static, the electric and magnetic fields from DC lines do not induce currents and voltages.

### Does AC produce emf?

AC electric power produces electric and magnetic fields that create weak electric currents in humans. Being exposed to some kinds of EMF may have some bad effects on humans, but scientists do not know for sure.

What is the purpose of back emf?

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.

#### What is the emf equation of dc motor?

As the armature rotates, a voltage is generated in its coils. In the case of a generator, the emf of rotation is called the Generated emf or Armature emf and is denoted as Er = Eg. In the case of a motor, the emf of rotation is known as Back emf or Counter emf and represented as Er = Eb.

What is DC EMF?

A Direct Current (DC) electromagnetic field refers to a constant or static DC electric or DC magnetic field emission which has a frequency of 0 Hz. DC magnetic fields can also be created from a DC power source of electricity such as battery power, solar power and wind power.

## What is the difference between magnetic field produced by direct current DC and alternating current AC )?

Both AC and DC describe types of current flow in a circuit. In direct current (DC), the electric charge (current) only flows in one direction. Electric charge in alternating current (AC), on the other hand, changes direction periodically.

What is DC emf?

### What is AC emf?

An AC electromagnetic field, also known as EMF or EM field, is a physical field produced by moving electrically charged objects. The field can be viewed as the combination of an AC electric field and an AC magnetic field. Since it is AC by definition, it continually changes polarity from positive to negative.

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. Circuit diagram and example taken from New South Wales, Department of Education and Training, 2007.

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

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.

What is the relation between supply and back EMF?

The relation between the main supply, back emf and armature current is given as E b = V – I a R a. 1. The back emf opposes the supply voltage. The supply voltage induces the current in the coil which rotates the armature. The electrical work required by the motor for causing the current against the back emf is converted into mechanical energy.

## Which is a stronger magnetic field AC or DC?

For the same value of current flowing through a purely resistive wire, the magnetic fields produced by AC or DC will be the same. If there’s a capacitor or an inductor in the circuit, magnetic fields will be stronger for AC.

How does the magnitude of the back EMF decrease?

As the back emf depends on the current their value also decreases. The magnitude of the back EMF is nearly equal to the supply voltage. If the sudden load is applied to the motor, the motor becomes slow down. As the speed of the motor decreases, the magnitude of their back emf also falls down.