When the number of turns in a coil is doubled without any change in the length of the coil,its self-inductance

$A$ long solenoid has $1000$ turns. When a current of $4\, A$ flows through it,the magnetic flux linked with each turn of the solenoid is $4 \times 10^{-3}\, Wb$. The self-inductance of the solenoid is......$H$

The current passing through a choke coil of $5 \, H$ is decreasing at the rate of $2 \, A/s$. The $e.m.f.$ developed across the coil is ....... $V$.

In a fluorescent lamp choke (a small transformer),$100 \; V$ of reverse voltage is produced when the choke current changes uniformly from $0.25 \; A$ to $0 \; A$ in a duration of $0.025 \; ms$. The self-inductance of the choke (in $mH$) is estimated to be:

$A$ solenoid of length $l$ metre has self-inductance $L$ henry. If the number of turns is doubled,its self-inductance becomes:

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 $\text{ V}$)