$A$ coil having $N$ turns is wound tightly in the form of a spiral with inner and outer radii $a$ and $b$ respectively. When a current $i$ passes through the coil,the magnetic field at the centre is

  • A
    $\frac{\mu_0 Ni}{b}$
  • B
    $\frac{2\mu_0 Ni}{a}$
  • C
    $\frac{\mu_0 Ni}{2(b - a)} \ln\left(\frac{b}{a}\right)$
  • D
    $\frac{\mu_0 Ni}{(b - a)} \ln\left(\frac{b}{a}\right)$

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$A$ circular arc of radius $r$ carrying current $I$ subtends an angle $\frac{\pi}{8}$ at its centre. The radius of the metal wire is uniform. The magnetic induction at the centre of the circular arc is ($\mu_0 =$ permeability of free space).

$A$ long straight wire carrying a current of $30 \ A$ is placed in an external uniform magnetic field of induction $4 \times 10^{-4} \ T$. The magnetic field is acting parallel to the direction of current. The magnitude of the resultant magnetic induction in tesla at a point $2.0 \ cm$ away from the wire is $(\mu_0 = 4 \pi \times 10^{-7} \ H/m)$.

The magnetic field at the centre of a circular coil of radius $r$,through which a current $I$ flows,is:

$A$ plastic disc of radius $R$ has a charge $q$ uniformly distributed over its surface. If the disc is rotated at an angular frequency $\omega$ about its axis,the magnetic induction at the center of the disc is:

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View Solution

$1 \ T = \dots \text{Gauss}$.

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