Work Step by Step
The magnetic field direction is always perpendicular to the direction in which the EM wave is traveling and is also perpendicular to the electric field. North and south are the only possibilities. To choose between them, use the right-hand rule. Point the fingers of your right hand in the direction of the E field (west), then curl them until they point in the direction of the B field (north). Your thumb then points in the direction of the traveling wave (down into the ground).