Chhattisgarh PMT Chhattisgarh PMT Solved Paper-2007

  • question_answer
    Two wires of same material and same lengths having cross-sections 3:1. If resistance of thicker wire is \[10\,\Omega \] and both are joined in series then equivalent resistance is

    A) \[10\,\Omega \]                                              

    B) \[20\,\Omega \]

    C) \[30\,\Omega \]                                              

    D) \[40\,\Omega \]

    Correct Answer: D

    Solution :

    Given \[{{A}_{1}}:{{A}_{2}}=3:1,\] \[{{R}_{1}}=10\Omega \] Resistance      \[(R)=\frac{\rho l}{A}\] \[\therefore \]  \[R\propto \frac{1}{A}\]                 \[\frac{{{R}_{1}}}{{{R}_{2}}}=\frac{{{A}_{2}}}{{{A}_{1}}}\]                 \[\frac{10}{{{R}_{2}}}=\frac{1}{3}\] \[\therefore \]  \[{{R}_{2}}=30\Omega \] In series,       \[R={{R}_{1}}+{{R}_{2}}\]                                 \[=10+30=40\Omega \]


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