Question

A rectangular frame through which current is flowing is placed in a uniform magnetic field so that its axis is perpendicular to the magnetic lines of force of the field (Fig.). Indicate the direction of the forces acting on sides BC and DA of the frame. Discuss the nature of the change in the magnitude of these forces with a change in the position of the frame during rotation.

Answer 1

The forces F₁ and F₂ attain their greatest value when the plane of the frame is perpendicular to the magnetic lines of force. The forces drop to zero when the plane of the frame is along the lines of force. When the frame rotates 180° from the position shown in Fig., the forces F₁ and F₂ reverse their directions and tend to compress the frame along its axis of rotation.