The drawing shows a wire composed of three segments, ab, bc, and cd. there is a current of i = 2.0 a in the wire. there is also a magnetic field b (magnitude = 0.25 t) that is the same everywhere and points in the direction of +z axis. the lengths of the wire segments are lab = 1.0 m, lbc = 0.7 m, and lcd = 0.7 m. find the magnitude of the force that acts on each segment.

The magnitude of the magnetic force acting on the wire is zero, because the magnetic field is parallel to the wire.

In fact, the magnetic force exerted by the magnetic field on the wire is

where I is the current in the wire, L the length of the wire, B the magnetic field intensity and  the angle between the direction of B and the wire. In our problem, B and the wire are parallel, so the angle is  and so , therefore the magnetic force is zero: F=0.