A long solenoid has 500 turns. When a current of 2 ~A is passed...

Key Idea : Inductance of a coil is numerically equal to the emf induced in the coil when the current in the coil changes at the rate of $1 \mathrm{As}^{-1}$. If $I$ is the current flowing in the circuit, then flux linked with the circuit is observed to be proportional to $I$, ie, $$\begin{aligned} & \phi \propto I \\ & \text{or } \phi=L I \end{aligned}$$ where $L$ is called the self-inductance or coefficient of self-inductance or simply inductance of the coil. Net flux through solenoid, $\phi=500 \times 4 \times 10^{-3}=2 \mathrm{~Wb} or 2=L \times 2$ [after putting values in Eq. or $L=1 \mathrm{H}$