The self-inductance of an air-cored solenoid of length $40 \ cm$,diameter $7 \ cm$ having $200$ turns is nearly: (in $\mu H$)

The current through a choke coil increases from zero to $6 \ A$ in $0.3 \ s$ and an induced $e.m.f.$ of $30 \ V$ is produced. The inductance of the choke coil is ....... $H$.

$A$ solenoid is tightly wound with wire of diameter $0.10\,cm$,has a cross-sectional area $\frac{1}{\pi}\,cm^2$,and is $40\,cm$ long. If the current through the solenoid decreases uniformly from $10\,A$ to $0\,A$ in $0.10\,s$,then the $emf$ induced inside the solenoid is.....$mV$.

$A$ coil and a bulb are connected in series with a $12 \,V$ direct current $(DC)$ source. $A$ soft iron core is now inserted into the coil. Then,

Current in a coil changes from $4 \,A$ to zero in $0.1 \,s$ and the emf induced is $100 \,V$. The self inductance of the coil is (in $\,H$)

$A$ $30\text{ cm}$ long solenoid has $10$ turns per cm and area of $5\text{ cm}^2$. The current through the solenoid coil varies from $2\text{ A}$ to $4\text{ A}$ in $3.14\text{ s}$. The e.m.f. induced in the coil is $\alpha \times 10^{-5}\text{ V}$. The value $\alpha$ is . . . . . . .