A long solenoid has $2000$ turns per metre. A small coil of $100$ turns, each of area $2\ \text{cm}^2$, sits inside it near its middle, with the same axis. The current in the solenoid is increased steadily at $50\ \text{A/s}$. Take $\mu_0 = 4\pi \times 10^{-7}\ \text{T m/A}$. The emf induced in the small coil is closest to