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CMC Medical CMC-Medical Ludhiana Solved Paper-2013

  • question_answer
    An electric motor run on DC source of emf 200 V and draws a current of 20 A. If the efficiency be 40%, then the resistance of armature is

    A)  \[2\,\Omega \]                               

    B)  \[8\,\Omega \]

    C)  \[12\,\Omega \]                             

    D)  \[6\,\Omega \]

    Correct Answer: C

    Solution :

                    Input power = VI \[=200\times 10\] \[=2000\,W\] Output power\[=\frac{40}{100}\times 2000\]            \[=800\,W\] Power loss in heating the armature         \[=2000-800\]         \[=1200\,W\] \[{{I}^{2}}R=1200\]    \[R=\frac{1200}{{{I}^{2}}}\]        \[=\frac{1200}{100}\]   \[R=12\,\Omega \]


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