Q98 / 120 · JEE Advanced 2006 · Physics

$$ \text { Which of the following statement is correct in Infinitely long wire kept perpendicular } $$ to the paper carrying current inwards the given figure? Figure

  • Correct answer
    A
    net force on the loop is zero
  • B
    net torque on the loop is zero
  • Correct answer
    C
    loop will rotate clockwise about axis $\mathrm{OO}^{\prime}$ when seen from $O$
  • D
    loop will rotate anti-clockwise about $\mathrm{OO}^{\prime}$ when seen from $O$

Solution

$\mathbf{F}_{B A}=0$, because magnetic lines are parallel to this wire. $\mathbf{F}_{C D}=0$, because magnetic lines are antiparallel to this wire. $\mathbf{F}_{C B}$ is perpendicular to paper inwards and $\mathbf{F}_{A D}$ is perpendicular to paper outwards. These two forces (although calculated by integration) cancel each other but produce a torque which tend to rotate the loop in clockwise direction about an axis $O O^{\prime}$.

Hence, the correct answer is options: 'A', 'C'.

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