$A$ closely wound flat circular coil of $25$ turns of wire has a diameter of $10\, cm$ and carries a current of $4\, A$. Determine the magnetic flux density at the centre of the coil.

$A$ circular arc of radius $r$ carrying current $I$ subtends an angle $\frac{\pi}{16}$ at its centre. The radius of the metal wire is uniform. The magnetic induction at the centre of the circular arc is [where $\mu_0$ is the permeability of free space].

$A$ coil of one turn is made of a wire of a certain length,and then from the same length of wire,a coil of two turns is made. If the same current is passed in both cases,what is the ratio of the magnetic inductions at their centers?

An infinitely long wire carrying current $I$ is along the $Y$-axis such that its one end is at point $A(0, b)$ while the wire extends up to $+\infty$. The magnitude of the magnetic field strength at point $(a, 0)$ is:

Two long straight parallel conductors carry currents $I_1$ and $I_2$ $(I_1 > I_2)$. When the direction of $I_1$ and $I_2$ is the same,the magnetic field intensity midway between the two conductors is $20 \mu T$. If the direction of $I_2$ is reversed,the field intensity becomes $50 \mu T$. The ratio $I_2 / I_1$ is:

$A$ steady electric current is flowing through a cylindrical wire. Which of the following statements is/are correct?
$(a)$ The electric field at the axis of the wire is zero.
$(b)$ The magnetic field at the axis of the wire is zero.
$(c)$ The electric field in the vicinity of the wire is zero.
$(d)$ The magnetic field in the vicinity of the wire is zero.