$A$ circular loop of radius $r$ is carrying current $I \ A$. The ratio of the magnetic field at the centre of the circular loop to the magnetic field at a distance $r$ from the centre of the loop on its axis is:

$A$ circular loop of radius $R$ is carrying current $I$. The ratio of the magnetic field at the center of the circular loop to the magnetic field at a distance $R$ from the center of the loop on its axis is:

$A$ long straight wire carrying current $16 \,A$ is bent at $90^{\circ}$ such that one segment lies along the positive $x$-axis and the other segment lies along the positive $y$-axis. What is the magnitude of the magnetic field at the point $P(-2 \,mm, 0)$ (in $\,mT$)? (Assume $\frac{\mu_0}{4 \pi} = 10^{-7} \,T \cdot m/A$)

The direction of magnetic lines of force produced by passing a direct current in a conductor is given by

The magnetic field at a distance $r$ from a long straight wire carrying current $I$ is $0.4 \text{ tesla}$. The magnetic field at a distance $2r$ will be (in $\text{ tesla}$)

The unit vectors $\hat{i}, \hat{j},$ and $\hat{k}$ are as shown below. What will be the magnetic field at $O$ in the following figure?