To measure a magnetic field between the magnetic poles of a loud speaker, a small coil having 30 turns and $2.5\,\text{cm}^2$ area is placed perpendicular to the field and removed immediately. If the total charge flown through the coil is $75 \times 10^{-3}\,\text{C}$ and the total resistance of wire and galvanometer is $0.3\,\Omega$, then the magnitude of the magnetic field is