Self-induction of a solenoid cannot be increased by

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 $\text{ V}$)

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 ....... $V$.

When the number of turns in a solenoid are doubled without any change in the length of the solenoid,its self-inductance becomes

An air-cored solenoid with length $30 \ cm$,area of cross-section $25 \ cm^2$ and number of turns $500$ carries a current of $2.5 \ A$. The current is suddenly switched off for a brief time of $10^{-3} \ s$. How much is the (nearly) average back e.m.f. induced across the ends of the open switch in the circuit (in $V$)? (Ignore the variation of magnetic field near the ends of solenoid)

The self-induced $emf$ of a coil is $25\,V$. When the current in it is changed at a uniform rate from $10\,A$ to $25\,A$ in $1\,s$,the change in the energy stored in the inductor is......$J$.