10th Class Science Electricity and Circuits Question Bank Electricity

  • question_answer
    Two straight parallel wires, both carrying 10 amperes in the same direction attract each other with a force of \[\text{1 }\times \text{ 1}{{0}^{-\text{3}}}\] N. If both currents are doubled, then force of attraction will be

    A) \[\text{1 }\times \text{ 1}{{0}^{-\text{3}}}\text{ N}\]        

    B)         \[\text{2 }\times \text{ 1}{{0}^{\text{-3}}}\text{ N}\]

    C) \[~\text{4 }\times \text{ 1}{{0}^{-\text{3}}}\text{ N}\]          

    D)         \[0.\text{25 }\times \text{ 1}{{0}^{-\text{3}}}\text{ N}\]

    Correct Answer: C

    Solution :

                             \[F=\frac{{{\mu }_{0}}}{4\pi }\cdot l\frac{2{{i}_{1}}{{i}_{2}}}{d}\] \[\therefore \]  \[1\times {{10}^{-3}}=\frac{{{\mu }_{0}}}{4\pi }l\frac{2\times 10\times 10}{d}\]  ? (i) and                 \[F=\frac{{{\mu }_{0}}}{4\pi }l\frac{2\times 20\times 20}{d}\]            ? (ii) From equations (i) and (ii),                 \[\frac{1\times {{10}^{-3}}}{F}=\frac{\frac{{{\mu }_{0}}}{4\pi }l\frac{2\times 10\times 10}{d}}{\frac{\mu }{4\pi }\frac{2\times 20\times 20}{d}}=\frac{10\times 10}{20\times 20}\] \[\therefore \]           \[\mathbf{F=4\times 1}{{\mathbf{0}}^{\mathbf{-3}}}\mathbf{N}\].


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