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12th Class Physics Magnetic Effects of Current / करंट का चुंबकीय प्रभाव Question Bank MCQs - Magnetism and Matter

  • question_answer
    Consider the two idealized systems: (i) a parallel plate capacitor with large plates and small separation and (ii) a long solenoid of length L, R, radius of cross-section. In (i), E is ideally treated as a constant between plates and zero outside, In (ii), magnetic field is constant inside the solenoid and zero outside. These idealized assumptions, however, contradict fundamental laws as below :

    A) Case (i) contradicts Gauss's law for electrostatic fields.

    B) Case (ii) contradicts Gauss's law for magnetic fields.

    C) Case (i) agrees with \[\oint{_{s}E.dl=0}\]

    D) Case (ii) contradicts \[\oint{H.dl={{I}_{en}}}\]

    Correct Answer: B

    Solution :

    Option [b] is correct.
    Explanation: According to Gauss's law of electrostatic field, \[\operatorname{O}\int E.dl=\frac{q}{{{\varepsilon }_{0}}}\]
    So it does not contradict for electrostatic field as the electric field lines do not form continuous path.
    According to Gauss's law of magnetic field, \[\operatorname{O}\int \operatorname{B}.ds=0\]
    It is clear that it contradicts for magnetic field because there is magnetic field inside the solenoid, and no field outside the solenoid carrying current, but the magnetic field lines form the closed paths.


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