It is desired to measure the magnitude of field between the poles of a powerful loud speaker magnet. A small flat search coil of area $2cm^2$ with closely wound turns, is positioned normal to the field direction and then quickly snatched out of the field region. Equivalently one can give it a quick $90^{\circ}$ turns to bring its plane parallel to the field direction. The total change flown in the coil (measured by a ballistic galvanometer connected to coil) is 7.5mc. The combined resistance of the coil and the galvanometer $0.50 \Omega$. Estimate the field strength of magnet.
