- 16-Jul-2022

**Induced emf is also called back emf** because, the induced emf opposes the change in current, due to the source of emf.

For a DC motor, magnitude of the back emf is given by the same emf equation of a dc generator i.e. **Eb = PɸNZ / 60A**.

Back-EMF is **the electric potential difference that opposes the current that induces it**. When the magnetic field collapses in a conductor,this back E.M.F. is generated in accordance with lenz's law.

We can calculate the back EMF by **measuring the current in steady state with no load and comparing it to a calculated value for the stall current**. We can then use this value with the no-load speed and the motor's constants to calculate the speed for the given back EMF.

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. And that energy is induced in the armature of the motor.

**Yes, it is true that induced emf has no direction of its own**. Because if the magnetic flux in a circuit increases, the direction of induced emf will be such as to decrease the flux. If the magnetic flux in a circuit decreases then the direction of induced current will be such as to increase the flux.

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.

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. This implies the current needs to do work against back Emf.

We use Faraday's law of induction to find the average emf induced over a time Δt: **emf=−NΔΦΔt** emf = − N Δ Φ Δ t . We know that N = 200 and Δt = 15.0 ms, and so we must determine the change in flux ΔΦ to find emf.

It is **the phenomenon of production of e.m.f. in a conductor due to a change in magnetic flux linked with it**. The e.m.f so produced is called induced e.m.f. and current is called induced current.

Back EMF is **the system in the coil of an electric motor that opposes the current flowing through the coil, when the armature rotates**. When the speed varies, the winding characteristics may fluctuate, resulting in variation of back EMF.

The induced emf is sometimes called back emf **because it opposes the change in current , due to the source of the emf**.

When the armature of the DC motor rotates under the influence of driving torque, the armature of the conductors moves through a magnetic field inducing an emf in them. **The induced emf is in the opposite direction to the applied voltage** and is known as the back emf.

Back emf is **the generator output of a motor**, and so it is proportional to the motor's angular velocity ω. It is zero when the motor is first turned on, meaning that the coil receives the full driving voltage and the motor draws maximum current when it is on but not turning.

The Formula for Calculating the EMF

If we know the resulting energy and the amount of charge passing through the cell. It is the simplest way to calculate the EMF. Instead, we may use the definition more like the Ohm's law i.e V = IR. So the formula is, **\varepsilon = I (R+r)**

Back electromotive force is the voltage generated at both ends of a winding due to changes in flux linkage in a shaft motor operation. Since the back electromotive force is proportional to the moving speed, it is a constant. The unit is .

The electromagnet will store energy when powered and will generate a “back EMF”, or counter EMF (CEMF), **when the supply is switched off**. When the supply is connected current is flowing through the windings of the electromagnet coil.

Back emf is the voltage drop in an alternating current (AC) circuit caused by magnetic induction. For example, **the voltage drop across an inductor is due to the induced magnetic field inside the coil**. The voltage's polarity is at every moment the reverse of the input voltage.

**Induced emf is also called back emf** because, the induced emf opposes the change in current, due to the source of emf.

Derivation of EMF Equation of DC Generator

(1), that for any dc generator Z, P and A are constant so that **E _{g} ∝ N_{ϕ}**. Therefore, for a given DC generator, the induced EMF in the armature is directly proportional to the flux per pole and speed of rotation.

**Self-induction of coil is the property by virtue of which it tends to maintain the magnetic flux linked with it and opposes any change in the flux by inducing current in it**. This property of a coil is analogous to mechanical inertia. That is why self-induction is called the inertia of electricity.

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