$A$ direct current $I$ flows along the length of an infinitely long straight thin-walled pipe. Then the magnetic field is

The magnetic induction produced inside an ideal solenoid depends on which of the following quantities?
$(a)$ Number of turns per unit length $(n)$.
$(b)$ Radius of the wire.
$(c)$ Current flowing through it $(I)$.
$(d)$ Permeability of the medium $(\mu)$.

"On flowing current in a conducting wire, a magnetic field is produced around it." This is a law of

The relative permeability in a core of a solenoid is $400$. The windings of a solenoid are insulated from the core and carry a current of $2 \ A$. If the number of turns is $1000$ per meter,then the magnetic intensity inside the core of the solenoid is . . . . . . $\frac{A}{m}$.

Inductance per unit length near the middle of a long solenoid is ($\mu_0=$ permeability of free space,$n=$ number of turns per unit length,$d=$ the diameter of the solenoid).

$A$ solenoid has a core made of material with relative permeability $400$. The magnetic field produced in the interior of the solenoid is $1.0 \text{ T}$. The magnetic intensity in $SI$ units is $\alpha \times 10^5$. The value of $\alpha$ is . . . . . . . (Free space permeability $\mu_0 = 4\pi \times 10^{-7} \text{ SI units}$.)