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RAJASTHAN PMT Rajasthan - PMT Solved Paper-2002

  • question_answer
     n equal cells having e.m.f. E and internal resistance r, are connected in circuit of a resistance R. Same current flows in circuit either they connected in series or parallel, if:

    A)  \[R=nr\]             

    B)         \[R=\frac{r}{n}\]

    C)  \[R={{n}^{2}}r\]              

    D)         \[R=r\]

    Correct Answer: D

    Solution :

    Current when cells are connected in series \[{{i}_{s}}=\frac{nE}{nr+R}\] In parallel            \[{{i}_{P}}=\frac{nE}{r+nR}\] According to question \[{{i}_{s}}={{i}_{p}}\]                                 \[\frac{nE}{nr+R}=\frac{nE}{r+nR}\]                                 \[r+nR=nr+R\]                                 \[(n-1)R=r(n-1)\] \[\Rightarrow \]                         \[R=r\]


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