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NEET Sample Paper NEET Sample Test Paper-28

  • question_answer
    A potentiometer wire of length 100 cm has a resistance of \[10\Omega \]. It is connected in series with a resistance and a cell of emf 2V and of negligible internal resistance. A source of emf \[10mV\] is balanced against a length of 40 cm of the potentiometer wire. What is the value of external resistance :-

    A)  \[810\,\Omega \]                           

    B)  \[790\,\Omega \]

    C)  \[1020\,\Omega \]                        

    D)  \[480\,\Omega \]

    Correct Answer: B

    Solution :

    Balanced \[V=x\]\[\times \]  Balancing length \[10\times {{10}^{-3}}=x\times 40\times {{10}^{-2}}\] \[x=\frac{1}{40}V/m\] Now \[x=\frac{{{I}_{\omega }}{{R}_{\omega }}}{{{L}_{\omega }}}\] \[\left( \frac{2}{10+R} \right).\frac{10}{1}=\frac{1}{40}\] \[10+R=800\] \[R=790\Omega \]


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