Suppose an isolated north pole is kept at the centre of a circular loop carrying a electric current $i$. The magnetic field due to the north pole at a point on the periphery of the wire is $B$. The radius of the loop is $a$. The force on the wire is
ANearly $2 \pi a i B$ perpendicular to the plane of the wire
B$2 \pi a i B$ in the plane of the wire
C$\pi a i B$ along the axis of the wire
D$0$
Medium
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ANearly $2 \pi a i B$ perpendicular to the plane of the wire
a (a)
$d F=I d I B$
$F_{\text {total }}=i(2 \pi a) B$
Perpendicular to the plane of the paper.
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