JEE Main & Advanced JEE Main Paper (Held on 09-4-2019 Afternoon)

  • question_answer
    Two coils 'P' and 'Q' are separated by some distance. When a current of 3 A flows through coil 'P', a magnetic flux of \[{{10}^{-3}}\]Wb passes through 'Q'. No current is passed through 'Q'. When no current passes through 'P' and a current of 2 A passes through 'Q', the flux through 'P' is:-          [JEE Main 9-4-2019 Afternoon]

    A) \[6.67\times {{10}^{3}}Wb\]          

    B) \[6.67\times {{10}^{4}}Wb\]

    C) \[3.67\times {{10}^{4}}Wb\]          

    D) \[3.67\times {{10}^{3}}Wb\]

    Correct Answer: B

    Solution :

    \[{{\phi }_{q}}=\frac{{{\mu }_{0}}{{i}_{1}}{{R}^{2}}}{2{{({{R}^{2}}+{{x}^{2}})}^{\frac{3}{2}}}}\times \pi {{r}^{2}}={{10}^{-3}}\]           \[{{\phi }_{p}}=\frac{{{\mu }_{0}}{{i}_{2}}{{r}^{2}}}{2{{({{r}^{2}}+{{x}^{2}})}^{\frac{3}{2}}}}\times \pi {{R}^{2}}\]           \[\frac{{{\phi }_{p}}}{{{\phi }_{Q}}}=\frac{{{i}_{2}}}{{{i}_{1}}}.\frac{{{({{R}^{2}}+{{x}^{2}})}^{\frac{3}{2}}}}{{{({{r}^{2}}+{{x}^{2}})}^{\frac{3}{2}}}}=\frac{{{\phi }_{p}}}{{{10}^{-3}}}\]           \[\frac{2}{3}=\frac{{{\phi }_{p}}}{{{10}^{-3}}}\] \[{{\phi }_{p}}=6.67\times {{10}^{-4}}\].


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