$A$ toroid has a number of turns per unit length $n$ and current $i$. What is the magnetic field inside the toroid?

The number of turns per unit length of a long solenoid is $10 \, \text{turns/cm}$. If its average radius is $5 \, \text{cm}$ and it carries a current of $10 \, \text{A}$, then the ratio of flux densities obtained at the centre and at the end on the axis will be:

$A$ long solenoid with $ 40 $ turns per cm carries a current of $ 1 \,A $. The magnetic energy stored per unit volume is $ J m^{-3} $. (in $\pi$)

$A$ solenoid of length $0.5 \,m$ has a radius of $1 \,cm$ and is made up of $m$ number of turns. It carries a current of $5 \,A$. If the magnitude of the magnetic field inside the solenoid is $6.28 \times 10^{-3} \,T$, then the value of $m$ is:

$A$ closely wound solenoid of $80 \,cm$ long has $5$ layers of windings of $400$ turns each. The diameter of the solenoid is $1.8 \,cm$. If the current carried is $8 \,A$, then the magnitude of the magnetic field inside the solenoid near its centre is approximately

If a long hollow copper pipe carries a current,then the magnetic field is produced: