JEE Advanced · Physics · 20. Magnetism & Current
Which of the following statement is correct in Infinitely long wire kept perpendicula to the paper carrying current inwards the given figure?

- A net force on the loop is zero
- B net torque on the loop is zero
- 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 \(O\)
Answer & Solution
Correct Answer
(C) loop will rotate clockwise about axis \(\mathrm{OO}^{\prime}\) when seen from \(O\)
Step-by-step Solution
Detailed explanation
\(\mathbf{F}_{B A}=0\), 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 \(O O^{\prime}\).
\(\mathbf{F}_{C D}=0\), 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 \(O O^{\prime}\).
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