A coil of $100$ turns, each of area $0.01\ \text{m}^2$, has a total resistance of $2\ \Omega$, and its ends are joined to make a closed circuit. A uniform magnetic field of $0.5\ \text{T}$ passes through the coil, perpendicular to its plane. The field is switched off and falls to zero. The total charge that flows round the coil, in millicoulombs, is ____.