At what distance on the axis, from the centre of a circular current carrying coil of radius $r$, the magnetic field becomes $1 / 8$ th of the magnetic field at centre?

  • A

    $\sqrt{2} r$

  • B

    $2^{3 / 2} r$

  • C

    $\sqrt{3} r$

  • D

    $3 \sqrt{2} r$

Similar Questions

Two concentric circular loops, one of radius $R$ and the other of radius $2 R$, lie in the $x y$-plane with the origin as their common center, as shown in the figure. The smaller loop carries current $I_1$ in the anti-clockwise direction and the larger loop carries current $I_2$ in the clockwise direction, with $I_2>2 I_1 . \vec{B}(x, y)$ denotes the magnetic field at a point $(x, y)$ in the $x y$-plane. Which of the following statement($s$) is(are) current?

$(A)$ $\vec{B}(x, y)$ is perpendicular to the $x y$-plane at any point in the plane

$(B)$ $|\vec{B}(x, y)|$ depends on $x$ and $y$ only through the radial distance $r=\sqrt{x^2+y^2}$

$(C)$ $|\vec{B}(x, y)|$ is non-zero at all points for $r$

$(D)$ $\vec{B}(x, y)$ points normally outward from the $x y$-plane for all the points between the two loops

  • [IIT 2021]

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