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A PMMDC motor has an armature resistance of 4.2 ohms. When 6 V supply is applied to motor it runs at 1215 rpm drawing 14.5 mA on no-load. The rotational losses is?

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A PMMDC motor has an armature resistance of 4.2 ohms. When 6 V supply is applied to motor it runs at 1215 rpm drawing 14.5 mA on no-load. The rotational losses is?

(a) 86.1 mW

(b) 86.1 W

(c) 8.6 W

(d) 8.6 mW

I had been asked this question in examination.

Asked question is from Permanent Magnet DC (PMDC) Motors topic in division DC Motors of Electrical Machines

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Correct answer is (a) 86.1 mW

To explain I would say: Rotational losses = E*Ia = 5.939* 14.5/1000 = 86.1 mW.

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