10th Class Science Electricity and Circuits Question Bank Electricity

  • question_answer
    The resistance of a metal wire of length 2 m is 400 at \[20{}^\circ C\]. If the diameter of the wire is 1 mm, what will be the resistivity of the metal at that temperature?

    A) \[1.28\times {{10}^{-8}}\Omega m\]     

    B) \[1.57\times {{10}^{-8}}\Omega m\]     

    C) \[1.75\times {{10}^{-9}}\Omega m\]     

    D) \[1.88\times {{10}^{-8}}\Omega m\]

    Correct Answer: B

    Solution :

    \[R=40\,\Omega ,d=1mm,I=2m\] \[\rho =\frac{RA}{I},\rho =\frac{R\pi {{d}^{2}}}{4I},\frac{40\times 2\times 1}{4\times 7\times 2\times {{10}^{8}}}=\frac{800}{56\times {{10}^{8}}}\] \[=\frac{880\times {{10}^{-8}}}{560}\]\[\therefore \]\[\rho =1.57\times {{10}^{-8}}\Omega m\]


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