The iambic trimeter derives its name from its essential shape, which is three metrical units (hence trimeter) which are each basically iambic in form. The iambic metron has the following shape (where the x is an anceps, the - is a longum, and the u is a brevis):
Hence, reversing the current running though a wire will have the affect of reversing the direction of the magnetic force at a point some distance away from the wire. The affect that this has on the overall magnetic field depends on the shape of the wire.
A current carrying conductor placed in a magnetic field experiences a force, whose magnitude is given by F=IlB in the direction opposite to that of the velocity of the rod. Now, consider an observer moving with the same velocity as that of the rod. For him, the charges are stationary. Yet, the rod experiences a force.