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12th Class Physics Magnetism Question Bank MCQs - Moving Charges and Magnetism

  • question_answer
    The strength of the magnetic field at distance r from a long straight current carrying wire is B. The field at a distance r/2 will be

    A) B

    B) 2B

    C) B/2

    D) B/4

    Correct Answer: B

    Solution :

    Option [b] is correct.
    Explanation: \[\operatorname{B}\propto 1/r\]
    \[{{\operatorname{B}}_{1}}/{{B}_{2}}={{r}_{2}}/{{r}_{1}}=\frac{r/2}{r}\] \[\therefore {{\operatorname{B}}_{2}}=2{{B}_{1}}=2B\]
     


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