2. Solved Papers
  3. Punjab Medical

Punjab Medical Punjab - MET Solved Paper-2007

  • question_answer
    A copper wire of length 1m and radius \[1mm\] is joined in series with an iron wire of length \[2m\] and radius \[3mm\] and a current is passed through the wires. The ratio of the current density in the copper and iron wires is

    A) \[18:1\]                               

    B) \[9:1\]

    C) \[6:1\]                                  

    D) \[2:3\]

    Correct Answer: B

    Solution :

    Current density\[J=\frac{i}{A}=\frac{i}{\pi {{r}^{2}}}\] \[\Rightarrow \]               \[\frac{{{J}_{1}}}{{{J}_{2}}}=\frac{{{i}_{1}}}{{{i}_{2}}}\times \frac{r_{2}^{2}}{r_{1}^{2}}\] But the wires are in series, so they have the same current, hence,\[{{i}_{1}}={{i}_{2}}\] So,          \[\frac{{{J}_{1}}}{{{J}_{2}}}=\frac{r_{2}^{2}}{r_{1}^{2}}=9:1\]


You need to login to perform this action.
You will be redirected in 3 sec spinner