JIPMER Jipmer Medical Solved Paper-2010

  • question_answer
    A uniform wire of resistance \[R\] and length \[L\] is cut into four equal parts, each of length \[L\text{/}4,\]which are then connected in parallel combination. The effective resistance of the combination will be

    A)  \[R\]       

    B)                         \[4R\]                  

    C)  \[\frac{R}{4}\]                

    D)         \[\frac{R}{16}\]

    Correct Answer: D

    Solution :

    \[R=\frac{\rho l}{A}\] or \[R\propto l\] \[\therefore \]  \[\frac{{{R}_{1}}}{{{R}_{2}}}=\frac{{{l}_{1}}}{{{l}_{2}}}=\frac{L}{L\text{/}4}=4\] or            \[{{R}_{2}}=\frac{R}{4}\]                                               \[(\because \,{{R}_{1}}=R)\] In parallel combination of such four resistances. \[\frac{1}{R}=\frac{1}{{{R}_{2}}}+\frac{1}{{{R}_{2}}}+\frac{1}{{{R}_{2}}}+\frac{1}{{{R}_{2}}}\] or            \[\frac{1}{R}=\frac{1}{R\text{/}4}+\frac{1}{R\text{/}4}+\frac{1}{R\text{/}4}+\frac{1}{R\text{/}4}\] or            \[\frac{1}{R}=\frac{4}{R}+\frac{4}{R}+\frac{4}{R}+\frac{4}{R}\] or            \[\frac{1}{R}=\frac{16}{R}\] or            \[R=\frac{R}{16}\]


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