The current in a coil of inductance $5\, H$ decreases at the rate of $2\, A/s$. The induced $e.m.f.$ is....$V$

The inductance of a close-packed coil of $400$ turns is $8 \, mH$. $A$ current of $5 \, mA$ is passed through it. The magnetic flux through each turn of the coil is

$A$ solenoid of radius $R$ has $n$ turns per unit length. The self-inductance of the solenoid per unit length is:

To manufacture a solenoid of length $1 \,m$ and inductance $1 \,mH$, the length of thin wire required is (cross-sectional diameter of a solenoid is considerably less than the length).

$A$ hollow cylinder has length $l$,radius $r$,and thickness $d$,where $l >> r >> d$,and is made of a material with resistivity $\rho$. $A$ time-varying current $I$ flows through the cylinder in the tangential direction. Assume the current is always uniformly distributed along the length of the cylinder. The cylinder is fixed so that it cannot move; assume that there are no externally generated magnetic fields during the time considered for the problems below. Assume current at $t = 0$ to be $I_0$. What is the current $I(t)$ for $t > 0$?

The current in an inductor of self-inductance $L=40 \text{ mH}$ is to be increased uniformly from $2 \text{ A}$ to $12 \text{ A}$ in $8 \text{ ms}$. The emf induced in the inductor during this process is (in $\text{ V}$)