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.
Magnetic Field: This refers to an area encompassing a magnet or electric current which has the ability to attract or repel certain objects anywhere within the field. Magnetic Field (Earth's): The Earth's magnetic field is aligned with the north and south poles, and has reversed many times during geologic history.