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A dc motor has an armature resistance of 20 a9. When connected to a 220 V dc source, it takes a current of 1.5 A. What is the back emf developed in the motor?

1. 150 V
2. 170 V
3. 180 V
4. 190 V

Correct answer: 190 V

Solution

The back emf can be calculated using the formula: Back emf = Supply voltage - (Armature current x Armature resistance). Substituting the values, we get Back emf = 220 V - (1.5 A x 20 Ω) = 220 V - 30 V = 190 V, confirming that option D is correct.

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