Magnetics 4 Question 13
14. Which of the following statement is (are) correct in the given figure?
(2006, 5M)
Infinitely long wire kept
perpendicular to the paper
carrying current inwards
(a) Net force on the loop is zero
(b) Net torque on the loop is zero
(c) Loop will rotate clockwise about axis $O O^{\prime}$ when seen from $O$
(d) Loop will rotate anticlockwise about $O O^{\prime}$ when seen from $O$
Fill in the Blanks
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Answer:
Correct Answer: 14. (a, c)
Solution:
- $\quad \mathbf{F} _{B A}=0$, because magnetic lines are parallel to this wire. $\mathbf{F} _{C D}=0$, because magnetic lines are anti-parallel to this wire.
$\mathbf{F} _{C B}$ is perpendicular to paper outwards and $\mathbf{F} _{A D}$ is perpendicular to paper inwards. 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 $O O^{\prime}$.
