$A$ current $i$ is uniformly distributed over the cross section of a long hollow cylindrical wire of inner radius $R_1$ and outer radius $R_2$. The magnetic field $B$ varies with distance $r$ from the axis of the cylinder as:

$A$ toroid has a core (non-ferromagnetic) of inner radius $25 \; cm$ and outer radius $26 \; cm,$ around which $3500$ turns of a wire are wound. If the current in the wire is $11 \; A$,what is the magnetic field:
$(a)$ outside the toroid,
$(b)$ inside the core of the toroid,and
$(c)$ in the empty space surrounded by the toroid?

The expression for magnetic induction inside a solenoid of length $L$ carrying a current $I$ and having $N$ number of turns is

$A$ solenoid of $1200$ turns is wound uniformly in a single layer on a glass tube $2\,m$ long and $0.2\,m$ in diameter. The magnetic intensity at the center of the solenoid when a current of $2\,A$ flows through it is:

$A$ current of $2\, A$ flows in a long,straight wire of radius $2\, mm$. The intensity of the magnetic field on the axis of the wire is:

There is a long cylindrical pipe wire of internal radius $r$ and external radius $R$ carrying current $i$ along its length. The variation of magnetic field with distance from the axis of the wire can be represented by the :-