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NEET Physics Current Electricity, Charging & Discharging Of Capacitors / वर्तमान बिजली, चार्ज और कैपेसिटर का निर NEET PYQ-Current Electricity Charging Capacitors

  • question_answer
    A potentiometer wire has length 4 m and resistance \[8\,\,\Omega \]. The resistance that must be connected in series with the wire and an accumulator of emf 2V, so as to get a potential gradient 1 mV per cm on the wire is      [NEET  2015]

    A)  \[32\,\,\Omega \]           

    B)       \[40\,\,\Omega \]

    C)  \[44\,\,\Omega \]           

    D)       \[48\,\,\Omega \]

    Correct Answer: A

    Solution :

    [a] Given, \[1=4\text{ }m,\]
    \[R=\] potentiometer wire resistance \[=8\,\Omega \]
    Potential gradient \[\frac{dV}{dr}=1mV/cm\]
    So, for \[400cm,\Delta V=400\times 1\times {{10}^{-3}}=0.4V\]
    Let a resistor \[{{R}_{s}}\] connected in series, so as
    \[\Delta V=\frac{V}{R+{{R}_{s}}}\times R\]
    \[\Rightarrow \]   \[0.4=\frac{2}{8+R}\times 8\Rightarrow 8+R=\frac{16}{0.4}=40\]
    \[\Rightarrow \]   \[R=32\,\Omega \]


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