The self-inductance of a coil depends on

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 in a coil of inductance $0.2 \,H$ changes from $5 \,A$ to $2 \,A$ in $0.5 \,s$. The magnitude of the average induced emf in the coil is (in $\,V$)

The self-inductance $L$ of a solenoid of length $l$ and area of cross-section $A$ increases . . . . . . (Here with a fixed number of turns $N$).

The self-inductance of a coil is $5 \, H$. If a current of $1 \, A$ changes to $2 \, A$ within $5 \, s$ through the coil,the magnitude of the induced $e.m.f.$ will be $... \, V$.

Consider a solenoid carrying current supplied by a $DC$ source with a constant $emf$ containing an iron core inside it. When the core is pulled out of the solenoid,the change in current will: