Problem 3.299

A small coil is introduced between the poles of an electromagnet so that its axis coincides with the magnetic field direction. The cross-sectional area of the coil is equal to $S=3.0 \mathrm{~mm}^{2}$, the number of turns is $N=60 .$ When the coil turns through $180^{\circ}$ about its diameter, a ballistic galvanometer connected to the coil indicates a charge $q=4.5 \mu \mathrm{C}$ flowing through it. Find the magnetic induction magnitude between the poles provided the total resistance of the electric circuit equals $R=40 \Omega$.