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Question

An electric motor runs on DC source of emf 200 V and draws a current of 10 A. If the efficiency be 40%, then the resistance of armature is

A
2Ω
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B
8Ω
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C
12Ω
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D
16Ω
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Solution

The correct option is D 12Ω
Input power =VI=200×10
=2000 W
Output power =40100×2000=800 W
Power loss in heating the armature
=2000800
=1200 W
I2R=1200
or R=1200I2
=120010×10
or R=12Ω.

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