Problem 3.254

A small coil $C$ with $N=200$ turns is mounted on one end of a balance beam and introduced between the poles of an electromagnet as shown in Fig. 3.70. The cross-sectional area of the coil is $S=1.0 \mathrm{~cm}^{2},$ the length of the arm $O A$ of the balance beam is $=30 \mathrm{~cm} .$ When there is no current in the coil the balance is int equilibrium. On passing a current $I=22 \mathrm{~mA}$ through the coil the equilibrium is restored by putting the additional counterweight of mass $\Delta m=60 \mathrm{mg}$ on the balance pan. Find the magnetic induction at the spot where the coil is located.