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WB JEE Medical WB JEE Medical Solved Paper-2006

  • question_answer
    An electric current passes through a long straight copper wire. At a distance 5 cm from the straight wire, the magnetic field is B. The magnetic field at 20 cm from the straight wire would be:

    A)  \[\frac{B}{6}\]                                 

    B)  \[\frac{B}{4}\]

    C)  \[\frac{B}{3}\]                                 

    D)  \[\frac{B}{2}\]

    Correct Answer: B

    Solution :

                     \[B=\frac{{{\mu }_{0}}I}{2\pi r}\] or            \[B\propto \frac{1}{r}\] or            \[\frac{{{B}_{2}}}{{{B}_{1}}}=\frac{{{r}_{1}}}{{{r}_{2}}}\] \[\therefore \]  \[\frac{{{B}_{2}}}{B}=\frac{5}{20}=\frac{1}{4}\] or            \[{{B}_{2}}=\frac{B}{4}\]


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