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CMC Medical CMC-Medical VELLORE Solved Paper-2012

  • question_answer
    An electric motor draws a current of 10 A when operated on 60 V DC supply. If the efficiency of the motor is 50%, then the resistance of the motor windings is

    A)  15\[\Omega \]                                

    B)  3\[\Omega \]

    C)  3\[\Omega \]                                   

    D)  6\[\Omega \]

    Correct Answer: C

    Solution :

                    Given; efficiency \[\eta =50%\] \[\therefore \]  \[e=\frac{E}{2}\] and        \[i=\frac{E-e}{2}\] \[\Rightarrow \]               \[i=\frac{E-E/2}{R}=\frac{E}{2R}\] \[\therefore \]  \[R=\frac{E}{2i}=\frac{60}{2\times 10}=3\,\Omega \]


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