CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2004

  • question_answer
    Three long straight wires A, B and C are carrying currents as shown in figure. Then the resultant force on B is directed:

    A)  perpendicular to the plane of paper and outward

    B)  perpendicular to the plane of paper and inward

    C)  towards A

    D)  towards C

    Correct Answer: D

    Solution :

    Since, the currents in the three wires are flowing in same direction so, the wire B will experience a force of attraction due to both wires A and C, So,          \[{{F}_{AB}}=\frac{{{\mu }_{0}}}{4\,\pi }\,.\,\frac{2{{i}_{A}}\,{{i}_{B}}}{d}\]                 \[=\frac{{{\mu }_{0}}}{4\,\pi }.\frac{2\times 1\times 2}{d}\]                 \[=\frac{4{{\mu }_{0}}}{4\,\pi d}\]                                                            ?. (i) and        \[{{F}_{CB}}=\frac{{{\mu }_{0}}}{4\,\pi }.\frac{2{{i}_{B}}\,{{i}_{C}}}{d}=\frac{{{\mu }_{0}}}{4\pi }\times \frac{2\times 2\times 3}{d}\]                 \[=\frac{12{{\mu }_{0}}}{4\,\pi \,d}\]                                      ?. (ii) As seen from eqs. (1) and (2) \[{{F}_{CB}}>{{F}_{AB}}\] hence, the net force of attraction will be directed towards wire C.


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