Problem 3.253

A copper wire with cross-sectional area \(S=2.5 \mathrm{~mm}^{2}\) bent to make three sides of a square can turn about a horizontal axis \(O O^{\prime}\) (Fig. 3.69). The wire is located in uniform vertical magnetic field. Find the magnetic induction if on passing a current \(I=16 \mathrm{~A}\) through the wire the latter deflects by an angle \(\theta=20^{\circ}\)