Two identical current-carrying coils with the same center are placed with their planes perpendicular to each other. If current $I = \sqrt{2} \text{ A}$ and the radius of the coil is $R = 1 \text{ m}$,then the magnetic field at the center is equal to (where $\mu_0$ is the permeability of free space).

The magnetic field at a perpendicular distance '$r$' from a long straight wire carrying current '$I$' is '$B$'. The magnetic field at a perpendicular distance '$2r$' from the same wire is:

$A$ helium nucleus makes a full rotation in a circle of radius $0.8 \ m$ in $2 \ s$. The value of the magnetic field $B$ at the centre of the circle will be

The magnitude of the magnetic field at $O$ due to a current-carrying loop as shown in the figure is, where $O$ is the center of two circular portions with radii $1 \, cm$ and $2 \, cm$ respectively. (Take the value of current $I = \frac{1.2}{\pi} \, A$)

Five long wires $A, B, C, D$ and $E$,each carrying current $I$ are arranged to form edges of a pentagonal prism as shown in the figure. Each carries current out of the plane of the paper.
$(a)$ What will be the magnetic induction at a point on the axis $O$? The axis is at a distance $R$ from each wire.
$(b)$ What will be the field if the current in one of the wires (say $A$) is switched off?
$(c)$ What if the current in one of the wires (say $A$) is reversed?

Find the magnetic induction at point $O$ in the given figure.