The radius of a circular ring of wire is $R$ and it carries a current of $I \, A$. At its centre,a smaller ring of radius $r$ with current $i$ and $N$ turns is placed. Assuming that the planes of the two rings are perpendicular to each other and the magnetic induction produced at the centre of the bigger ring is constant,then the torque acting on the smaller ring will be:

  • A
    $Ni\pi r^2 \times \left( \frac{\mu_0 I}{2R} \right)$
  • B
    zero
  • C
    $Ni r^2 \times \left( \frac{\mu_0 I}{2R} \right)$
  • D
    $Ni\pi r^2 \times \left( \frac{I^2}{2R} \right)$

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$A$ circular coil having $200$ turns,$2.5 \times 10^{-4} \text{ m}^2$ area and carrying $100 \mu\text{A}$ current is placed in a uniform magnetic field of $1 \text{ T}$. Initially,the magnetic dipole moment $(\vec{M})$ was directed along $\vec{B}$. The amount of work required to rotate the coil through $90^{\circ}$ from its initial orientation such that $\vec{M}$ becomes perpendicular to $\vec{B}$ is . . . . $\mu\text{J}$.

If $m$ is the magnetic moment and $B$ is the magnetic field,then the torque is given by

$A$ current-carrying loop is placed in a uniform magnetic field in four different orientations,$I$,$II$,$III$,and $IV$. Arrange them in the decreasing order of potential energy.

$A$ disc of radius $r$ carrying a positive charge $q$ is rotating with an angular speed $\omega$ in a uniform magnetic field $B$ about a fixed axis as shown in the figure,such that the angle made by the axis of the disc with the magnetic field is $\theta$. The torque applied by the axis on the disc is:

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$A$ current-carrying circular loop of radius $2 \text{ cm}$ with unit normal $\hat{n} = \frac{\hat{i} + \hat{j}}{\sqrt{2}}$ is placed in a magnetic field $\vec{B} = B_0(3\hat{i} + 2\hat{j})$. If $B_0 = 4 \times 10^{-3} \text{ T}$ and current $I = 100\sqrt{2} \text{ A}$, the torque experienced by the loop is . . . . . . $\text{N}\cdot\text{m}$. $(\pi = 3.14)$

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