RAJASTHAN PMT Rajasthan - PMT Solved Paper-2009

  • question_answer
    There are 50 turns of a wire in every cm length of a long solenoid. If 4 A current is flowing in the solenoid, the approximate value of magnetic field along its axis at an internal point and at one end will be respectively

    A)  \[\begin{align}   & \text{12}\text{.6 }\!\!\times\!\!\text{ 1}{{\text{0}}^{\text{-3}}}\text{Wb/}{{\text{m}}^{\text{2}}} \\  & \text{6}\text{.3 }\!\!\times\!\!\text{ 1}{{\text{0}}^{\text{-3}}}\text{Wb/}{{\text{m}}^{\text{2}}} \\ \end{align}\]

    B)         \[\begin{align}   & \text{12}\text{.6 }\!\!\times\!\!\text{ 1}{{\text{0}}^{\text{-3}}}\text{Wb/}{{\text{m}}^{\text{2}}} \\  & 25.1\times {{10}^{-3}}Wb/{{m}^{2}} \\ \end{align}\]

    C)  \[\begin{align}   & \text{25}\text{.1 }\!\!\times\!\!\text{ 1}{{\text{0}}^{\text{-3}}}\text{Wb/}{{\text{m}}^{\text{2}}} \\  & \text{12}\text{.6 }\!\!\times\!\!\text{ 1}{{\text{0}}^{\text{-3}}}\text{Wb/}{{\text{m}}^{\text{2}}} \\ \end{align}\]

    D)         \[\begin{align}   & \text{25}\text{.1 }\!\!\times\!\!\text{ 1}{{\text{0}}^{\text{-5}}}\text{Wb/}{{\text{m}}^{\text{2}}} \\  & \text{12}\text{.6 }\!\!\times\!\!\text{ 1}{{\text{0}}^{\text{-5}}}\text{Wb/}{{\text{m}}^{\text{2}}} \\ \end{align}\]

    Correct Answer: C

    Solution :

    Given,\[N=50\,\,turns/cm=5000\,\,turns/cm\]                 \[I=4A\] Magnetic field at an internal point\[={{\mu }_{0}}nI\]                 \[=4\pi \times {{10}^{-7}}\times 5000\times 4\]                 \[=25.12\times {{10}^{-3}}Wb/{{m}^{2}}\] Magnetic field at one end\[=\frac{{{\mu }_{0}}nI}{2}\]                                                    \[=\frac{25.12\times {{10}^{-3}}}{2}\]                                                  \[=12.56\times {{10}^{-3}}Wb/{{m}^{2}}\]


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