A shunt dynamo has an armature resistance of 0.120 Ω.(a) If it is connected across 220 -V mains

step 1 In this given problem, armature resistance of this machine which is used as a shunt motor, that

A shunt dynamo has an armature resistance of 0.120 Ω.(a) If...

A shunt dynamo has an armature resistance of $0.120 \Omega .(a)$ If it is connected across 220 -V mains and is running as a motor, what is the induced (back) emf when the armature current is $50.0 \mathrm{~A}$ ? (b) If this machine is running as a generator, what is the induced emf when the armature is delivering $50.0 \mathrm{~A}$ at $220 \mathrm{~V}$ to the shunt field and external circuit?

A shunt dynamo has an armature resistance of $0.120 \Omega .(a)$ If it is connected across 220 -V mains and is running as a motor, what is the induced (back) emf when the armature current is $50.0 \mathrm{~A}$ ?
(b) If this machine is running as a generator, what is the induced emf when the armature is delivering $50.0 \mathrm{~A}$ at $220 \mathrm{~V}$ to the shunt field and external circuit?

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Key Concepts

Back EMF

Back electromotive force (EMF) is the voltage induced by the rotating armature in a DC machine that opposes the applied voltage during motor operation or supports the terminal voltage during generator operation. It plays a critical role in determining the net voltage across the armature and consequently the current flowing through it.

Armature Resistance and Voltage Drop

The armature resistance causes a voltage drop that, when multiplied by the armature current using Ohm's law (V = IR), must be accounted for in the calculation of the effective voltage. In motor operation this drop is subtracted from the supply voltage to determine the induced EMF, while in generator operation it is added to the terminal voltage to yield the induced EMF.

DC Motor and Generator Operation

In a DC machine, the same device can operate as a motor or a generator. When running as a motor, the applied voltage drives current into the armature and the back EMF acts to oppose this applied voltage. In contrast, during generator operation, the mechanical input induces an EMF in the armature that must overcome the internal resistance drop and deliver the required terminal voltage to the load.

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