A long solenoid having $100$ turns per cm carries a current of $\frac{4}{\pi}\,\text{A}$. At the centre of it is placed a coil of $200$ turns of cross-sectional area $25\,\text{cm}^2$ having its axis parallel to the field produced by the solenoid. When the direction of the current in the solenoid is reversed within $0.04\,\text{s}$, the induced emf in the coil is