JEE Main & Advanced Physics Current Electricity, Charging & Discharging Of Capacitors / वर्तमान बिजली, चार्ज और कैपेसिटर का निर Question Bank Critical Thinking

  • question_answer
    The resistance of a wire of iron is 10 ohms and temp. coefficient of resistivity is \[5\times {{10}^{-3}}/{}^\circ C\]. At \[20{}^\circ C\] it carries 30 milliamperes of current. Keeping constant potential difference between its ends, the temperature of the wire is raised to \[120{}^\circ C\]. The current in milliamperes that flows in the wire is [MP PMT 1994]

    A)            20  

    B)            15

    C)            10  

    D)            40

    Correct Answer: A

    Solution :

               \[\frac{{{R}_{1}}}{{{R}_{2}}}=\frac{(1+\alpha {{t}_{1}})}{(1+\alpha {{t}_{2}})}\]Þ\[\frac{10}{{{R}_{2}}}=\frac{(1+5\times {{10}^{-3}}\times 20)}{(1+5\times {{10}^{-3}}\times 120)}\]Þ\[{{R}_{2}}\approx 15\Omega \] Also \[\frac{{{i}_{1}}}{{{i}_{2}}}=\frac{{{R}_{2}}}{{{R}_{1}}}\] Þ \[\frac{30}{{{i}_{2}}}=\frac{15}{10}\] Þ \[{{i}_{2}}=20\,mA\]


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