JEE Main & Advanced Sample Paper JEE Main Sample Paper-45

  • question_answer
    A time varying magnetic field is present in a cylindrical region of radius R as shown in the figure. A positive charge q is taken slowly from P to Q \[via\]two paths-first through POQ second through PAQ. Work done by external  agent in 1stpath is W1 and through 2nd path is W2, then \[\frac{{{W}_{1}}}{{{W}_{2}}}\] is                (To compute \[\frac{{{W}_{1}}}{{{W}_{2}}}\], various distances and time variation of B (magnetic field) must be known.)

    A)  zero    

    B)  infinite

    C)  one                    

    D)  information insufficient

    Correct Answer: A

    Solution :

     In taking charge from P to 0, one has to perform work against the force experienced by charge due to the induced electric field. The induced electric field is perpendicular to line POQ and hence \[{{W}_{1}}=0\], while to compute exact value of \[{{W}_{2}}\] various distances and variations of magnetic field with time must be known, but it can be predicted that \[{{W}_{2}}\] is non-zero. So, ratio \[\frac{{{W}_{1}}}{{{W}_{2}}}=0\].

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