J & K CET Medical J & K - CET Medical Solved Paper-2003

  • question_answer
    Current is flowing with a current density \[J=480\text{ }A/c{{m}^{2}}\] in a copper wire. Assuming that each copper atom contributes one free electron and given that: Avogadro number \[=6.0\times {{10}^{23}}\] atoms/mol Density of copper \[=\text{ }9.0\text{ }g/c{{m}^{3}}\] Atomic weight of copper \[=\text{ }64\text{ }g/mol\] Electronic charge \[=1.6\times {{10}^{-19}}C\] The drift velocity of electrons is :

    A)  1 mm/s                                               

    B)  2 mm/s

    C)  0.5 mm/s                           

    D)  0.36 mm/s

    Correct Answer: D

    Solution :

                     Drift velocity is the average velocity that a particle such as an electron, attains due to an electric field. It is given by \[{{v}_{d}}=\frac{I}{nqA}\] where\[I\]is current, n the number of electrons, A the area, q the charge. Given,                 \[\frac{I}{A}=\frac{480A}{c{{m}^{2}}},q=1.6\times {{10}^{-19}}C\]                 \[n=\frac{6\times {{10}^{23}}\times 9}{64}\] \[\therefore \]  \[{{v}_{d}}=480\times \frac{64}{6\times {{10}^{23}}\times 9\times 1.6\times {{10}^{-19}}}\] \[\Rightarrow \] \[{{v}_{d}}=\frac{480\times 64}{6\times 9\times 1.6\times 10000}cm/s\] \[\Rightarrow \]               \[{{v}_{d}}=\frac{32}{900}cm/s\]                 \[=\frac{32\times 10}{900}mm/s\]                 \[=0.36\,mm/s\] \[\Rightarrow \]               \[{{v}_{d}}=0.36\,mm/s\]


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