VIT Engineering VIT Engineering Solved Paper-2008

  • question_answer
    A meter bridge is used to determine the resistance of an unknown wire by measuring the balance point length l. If the wire is replaced by another wire of same material but with double the length and half the thickness, the balancing point is expected to be

    A)  \[\frac{1}{8l}\]              

    B)  \[\frac{1}{4l}\]

    C)  \[8l\]             

    D)  \[16l\]  

    Correct Answer: C

    Solution :

    In a meter bridge the ratio of two resistances is \[\frac{R}{R}=\frac{l}{l}\] where \[l\] and \[l\] are balancing lengths Resistance \[R=\frac{\rho l}{A}=\frac{\rho l}{\pi {{r}^{2}}}\] If material remains same \[\rho =\rho \] Given      \[l=2l\] \[r=\frac{r}{2}\] \[\therefore \] \[R=\frac{\rho l}{A}\] \[=\frac{\rho 2l}{\pi {{\left( \frac{r}{2} \right)}^{2}}}\] \[=\frac{8\rho l}{\pi {{r}^{2}}}\] \[R=8R\] Therefore, the new balancing point is expected to be \[8l\].


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