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When the armature of a DC motor rotates, emf induced is
self-induced emf
mutually induced emf
back emf
none of the above
back emf
When a DC motor armature rotates within a magnetic field, the conductors cut the magnetic flux, inducing an EMF according to Faraday's Law of Electromagnetic Induction. This induced EMF acts in opposition to the applied supply voltage, hence it is termed 'Back EMF' (Eb).
When a DC motor armature rotates within a magnetic field, the conductors cut the magnetic flux, inducing an EMF according to Faraday's Law of Electromagnetic Induction. This induced EMF acts in opposition to the applied supply voltage, hence it is termed 'Back EMF' (Eb).
EbтАЛ=60AP╬жZNтАЛ тАФ Induced Back EMF in terms of machine constants
V=EbтАЛ+IaтАЛRaтАЛ тАФ Voltage balance equation for DC motor armature
As the motor rotates, the induced EMF (EbтАЛ) opposes the terminal voltage (V) applied to the armature. This relationship is defined by the Kirchhoff's Voltage Law equation V=EbтАЛ+IaтАЛRaтАЛ, where IaтАЛ is the armature current and RaтАЛ is the armature resistance. The back EMF acts as a self-regulating mechanism, controlling the amount of current drawn by the motor based on its load and speed.
The back EMF is always less than the applied terminal voltage (V>EbтАЛ).
At starting, the speed N=0, therefore EbтАЛ=0, leading to high starting current.
Lenz's Law explains the 'opposing' nature of the Back EMF.
Back EMF provides the inherent self-regulating property of a DC motor.
Automatic control of armature current based on load
Essential for stable operation of DC machines
Requires high starting current due to zero back EMF at start
Potential for commutator sparking if the machine is overloaded
DC series motors for traction
DC shunt motors for industrial drives
The magnitude of back EMF is proportional to speed (EbтАЛтИЭN).
Option A (self-induced emf) refers to inductance effects in a coil, whereas option B refers to transformer action.
C is correct тАФ The emf induced in the armature of a DC motor is called back emf because it opposes the applied supply voltage.
Remember that in a DC Generator, the induced EMF is the output voltage (generated EMF), while in a DC Motor, it is the Back EMF (opposing voltage).