$A$ long solenoid has a radius $a$ and the number of turns per unit length is $n$. If it carries a current $i$,then the magnetic field on its axis is directly proportional to

Choose the wrong statement to complete: An ideal solenoid has

$A$ toroid core has an inner radius of $0.24 \ m$ and an outer radius of $0.26 \ m$. $A$ current of $10 \ A$ flows through the wire having $2500$ turns around it. Find the magnetic field inside the core of the toroid.

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 . . . . . . $\frac{A}{m}$.

$A$ solenoid of length $0.5 \ m$ has a radius of $1 \ cm$ and is made up of $250$ turns. It carries a current of $5 \ A$. What is the magnitude of the magnetic field inside the solenoid?

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