Solution to task 419 from Chertov´s for extramural stud

419. A square frame made of thin wire can rotate freely around a horizontal axis coinciding with one of the sides. The mass m of the frame is 20 g. The frame was placed in a uniform magnetic field (B = 0.1 T) directed vertically upward. Determine the angle α by which the frame deviated from the vertical when a current I = 10 A was passed through it.